Ensure codemod mode ignores whitespace control.

`handlebars.parse` automatically applies whitespace control to the AST
before it is returned. For example, parsing the following template
([feel free to review the AST on
ASTExplorer](https://astexplorer.net/#/gist/f850c5457b808756107c0bc5ad226989/b0366df64be5c01b5f9eadd93e795b3b9d65d2c7)):

```hbs
 {{#foo}}
   {{~bar~}} {{baz~}}
 {{/foo}}
```

Using `Handlebars.parse`, the AST returned would have truncated the following whitespace:

* The whitespace prior to the `{{#foo}}`
* The newline following `{{#foo}}`
* The leading whitespace before `{{~bar~}}`
* The whitespace between `{{~bar~}}` and `{{baz~}}`
* The newline after `{{baz~}}`
* The whitespace prior to the `{{/foo}}`

A future version of `handlebars` (likely 4.5.0) will have a new method named
`parseWithoutProcessing`. When we update to that version we can remove
the custom workaround here.

packages/@glimmer/syntax/handlebars-shim.js

@@ -1,2 +1 @@
-import { parse } from './handlebars/compiler/base';
-export { parse };
+export { parse, parser as Parser } from './handlebars/compiler/base';

packages/@glimmer/syntax/lib/parser/tokenizer-event-handlers.ts

@@ -379,20 +379,26 @@ const syntax: Syntax = {
   Walker,
 };
 
+// emulate parseWithoutProcessing (from https://github.com/wycats/handlebars.js/pull/1584)
+// can be removed when we update to Handlebars 4.5.0
+function codemodParse(html: string, parseOptions?: HandlebarsParseOptions) {
+  // this sets up parser.yy and parser.yy.locInfo
+  handlebars.parse(html, parseOptions);
+
+  // casting to any here, because Parser is not listed in the types
+  return (handlebars as any).Parser.parse(html);
+}
+
 export function preprocess(html: string, options: PreprocessOptions = {}): AST.Template {
   let mode = options.mode || 'precompile';
 
   let ast: HBS.Program;
   if (typeof html === 'object') {
     ast = html;
+  } else if (mode === 'codemod') {
+    ast = codemodParse(html, options.parseOptions);
   } else {
-    let parseOptions = options.parseOptions || {};
-
-    if (mode === 'codemod') {
-      parseOptions.ignoreStandalone = true;
-    }
-
-    ast = handlebars.parse(html, parseOptions) as HBS.Program;
+    ast = handlebars.parse(html, options.parseOptions) as HBS.Program;
   }
 
   let entityParser = undefined;

packages/@glimmer/syntax/test/generation/print-test.ts

@@ -97,25 +97,19 @@ QUnit.module('[glimmer-syntax] Code generation - source -> source', function() {
   templates.forEach(buildTest);
 
   [
+    // custom HTML Entities
     '< &   > ©2018',
 
+    // whitespace control
+    '\n{{~var~}}  ',
+    '\n{{~#foo-bar~}} {{~else if x~}} {{~else~}} {{~/foo-bar~}}  ',
+
     // newlines after opening block
     '{{#each}}\n  <li> foo </li>\n{{/each}}',
-  ].forEach(buildTest);
-
-  test('whitespace control is preserved', function(assert) {
-    let before = '\n{{~var~}}  ';
-    let after = '{{~var~}}';
-
-    assert.equal(printTransform(before), after);
-  });
-
-  test('block whitespace control is preserved', function(assert) {
-    let before = '\n{{~#foo-bar~}} {{~else if x~}} {{~else~}} {{~/foo-bar~}}  ';
-    let after = '{{~#foo-bar~}}{{~else if x~}}{{~else~}}{{~/foo-bar~}}';
 
-    assert.equal(printTransform(before), after);
-  });
+    // "stand alone"
+    ' {{#foo}}\n  {{bar}}\n {{/foo}}',
+  ].forEach(buildTest);
 });
 
 QUnit.module('[glimmer-syntax] Code generation - override', function() {