Rework FileSystemDirectoryReader definition

Previously, FileSystemDirectoryReader IDL type was defined as having
an associated "directory reader" concept type, but (a) the properties
of that concept type were erroneously defined globally and (b) no
indirection from "this" to it's associated concept object to the
properties was done. Simplify by removing the concept object entirely,
and defining the properties as associated with the IDL type object,
properly scoped.

The association of an entry and directory was very loose and done
without naming the property. Explicitly name those.

No normative/observable behavior changes, just a (significant)
clarification in the text.

index.bs

@@ -175,16 +175,6 @@ note:
 The <dfn for=entry>file system</dfn> of an [=entry=] is the
 [=/file system=] associated with the [=entry=]'s [=entry/root=].
 
-<!-- ============================================================ -->
-## Directory Reader ## {#dir-reader}
-<!-- ============================================================ -->
-
-A <dfn>directory reader</dfn> consists of an associated [=directory
-entry=], an associated [=directory=] (initially null), a <dfn>reading
-flag</dfn> (initially unset), a <dfn>done flag</dfn> (initially
-unset), and a <dfn>reader error</dfn> (initially null).
-
-
 <!-- ============================================================ -->
 # Algorithms # {#algorithms}
 <!-- ============================================================ -->
@@ -632,11 +622,8 @@ entry=].
 
 The <dfn method for=FileSystemDirectoryEntry>createReader()</dfn> method steps are:
 
-1. Let |reader| be a new [=directory reader=] associated with the
-    [=directory entry=]'s [=directory=].
-
 1. Return a newly created {{FileSystemDirectoryReader}} object
-    associated with |reader|.
+    associated with [=directory entry=].
 
 </div>
 
@@ -754,60 +741,46 @@ interface FileSystemDirectoryReader {
 callback FileSystemEntriesCallback = undefined (sequence<FileSystemEntry> entries);
 </xmp>
 
-A {{FileSystemDirectoryReader}} has an associated [=directory reader=].
+<div dfn-for=FileSystemDirectoryReader>
+A {{FileSystemDirectoryReader}} has
+an associated <dfn>entry</dfn> (a [=directory entry=]),
+an associated <dfn>directory</dfn> (initially null),
+a <dfn>reading flag</dfn> (initially unset),
+a <dfn>done flag</dfn> (initially unset),
+and a <dfn>reader error</dfn> (initially null).
+</div>
 
 <div algorithm>
 
 The <dfn method for=FileSystemDirectoryEntry>readEntries(|successCallback|, |errorCallback|)</dfn> method steps are:
 
-1. If [=/this=]'s [=reading flag=] is set, [=queue a
-    task=] to [=invoke=] |errorCallback| with a newly
-    [=exception/created=] "{{InvalidStateError}}" {{DOMException}}, and abort these
-    steps.
+1. If [=/this=]'s [=FileSystemDirectoryReader/reading flag=] is set, [=queue a task=] to [=invoke=] |errorCallback| with a newly [=exception/created=] "{{InvalidStateError}}" {{DOMException}}, and abort these steps.
 
-1. If [=/this=]'s [=reader error=] is not null, [=queue
-    a task=] to [=invoke=] |errorCallback| (if given)
-    with [=reader error=], and abort these steps.
+1. If [=/this=]'s [=FileSystemDirectoryReader/reader error=] is not null, [=queue a task=] to [=invoke=] |errorCallback| (if given) with [=FileSystemDirectoryReader/reader error=], and abort these steps.
 
-1. If [=/this=]'s [=done flag=] is set, [=queue a
-    task=] to [=invoke=] |successCallback| with an empty
-    sequence and abort these steps.
+1. If [=/this=]'s [=FileSystemDirectoryReader/done flag=] is set, [=queue a task=] to [=invoke=] |successCallback| with an empty sequence and abort these steps.
 
-1. Set [=/this=]'s [=reading flag=].
+1. Set [=/this=]'s [=FileSystemDirectoryReader/reading flag=].
 
 1. [=Queue a task=] to perform the following steps:
 
-    1. Clear [=/this=]'s [=reading flag=].
-
-    1. Let |dir| be [=/this=]'s [=directory=].
+    1. Clear [=/this=]'s [=FileSystemDirectoryReader/reading flag=].
 
-    1. If |dir| is null, then:
+    1. If [=/this=]'s [=FileSystemDirectoryReader/directory=] is null, then:
 
-        1. Let |dir| be the result of [=evaluating
-            a path=] with [=/this=]'s [=entry/root=] and [=full path=].
+        1. Let |dir| be the result of [=evaluating a path=] with [=/this=]'s [=FileSystemDirectoryReader/entry=]'s [=entry/root=] and [=full path=].
 
-        1. If |dir| is failure, set [=/this=]'s
-            [=reader error=] to a newly [=exception/created=]
-            "{{NotFoundError}}" {{DOMException}}, [=invoke=] |errorCallback|
-            (if given) with [=reader error=], and abort these
-            steps.
+        1. If |dir| is failure, then set [=/this=]'s [=FileSystemDirectoryReader/reader error=] to a newly [=exception/created=] "{{NotFoundError}}" {{DOMException}}, [=invoke=] |errorCallback| (if given) with [=FileSystemDirectoryReader/reader error=], and abort these steps.
 
-        1. Set [=/this=]'s [=directory=] to |dir|.
+        1. Set [=/this=]'s [=FileSystemDirectoryReader/directory=] to |dir|.
 
-    1. Let |entries| be a non-zero number of entries from the
-        |dir| that have not yet been produced by this
-        [=directory reader=], if any.
+    1. Let |entries| be a non-zero number of entries from [=/this=]'s [=FileSystemDirectoryReader/directory=] that have not yet been produced by this {{FileSystemDirectoryReader}}, if any.
 
-    1. If the previous step failed (for example, the [=directory=] was
-        deleted or permission is denied), then set [=/this=]'s
-        [=reader error=] to an appropriate {{DOMException}},
-        [=invoke=] |errorCallback| (if given) with
-        [=reader error=], and abort these steps.
+    1. If the previous step failed (for example, the [=directory=] was deleted or permission is denied), then set [=/this=]'s [=FileSystemDirectoryReader/reader error=] to an appropriate {{DOMException}}, [=invoke=] |errorCallback| (if given) with [=FileSystemDirectoryReader/reader error=], and abort these steps.
 
-    1. If |entries| is empty, set [=/this=]'s [=done
-        flag=].
+    1. If |entries| is empty, set [=/this=]'s [=FileSystemDirectoryReader/done flag=].
 
-    1. [=invoke=] |successCallback| with |entries|.
+    1. [=Invoke=] |successCallback| with |entries|.
 
 </div>