Move rules from TypeScript lexer to TypeScript common module (#1530)

The TypeScript lexer was refactored in a previous commit to move its
memoisation methods into a module that could be mixed in by the TSX
lexer. This is because the TSX lexer needs to inherit from both the
TypeScript lexer and the JSX lexer but can't do that direclty because
Ruby does not support multiple inheritance.

While the memoisation methods were moved, changes to states of
TypeScript lexer were not refactored out. This means that the TypeScript
and TSX lexers can lex the same code differently. This commit fixes that
problem by adopting the same approach used with the ObjectiveC common
module: using Ruby's `Module#extended` hook.

lib/rouge/lexers/typescript.rb

@@ -18,17 +18,6 @@ class Typescript < Javascript
       filenames '*.ts', '*.d.ts'
 
       mimetypes 'text/typescript'
-
-      prepend :root do
-        rule %r/[?][.]/, Punctuation
-      end
-
-      prepend :statement do
-        rule %r/(#{Javascript.id_regex})(\??)(\s*)(:)/ do
-          groups Name::Label, Punctuation, Text, Punctuation
-          push :expr_start
-        end
-      end
     end
   end
 end

lib/rouge/lexers/typescript/common.rb

@@ -29,6 +29,19 @@ def builtins
           Pick Partial Readonly Record
         )
       end
+
+      def self.extended(base)
+        base.prepend :root do
+          rule %r/[?][.]/, base::Punctuation
+        end
+
+        base.prepend :statement do
+          rule %r/(#{Javascript.id_regex})(\??)(\s*)(:)/ do
+            groups base::Name::Label, base::Punctuation, base::Text, base::Punctuation
+            push :expr_start
+          end
+        end
+      end
     end
   end
 end