Update the spec parser to support enhanced parts

Change-Id: I6904294f473d1c9a861ad385e14e17bdd79189d8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/386560
Commit-Queue: Erik Ernst <eernst@google.com>
Reviewed-by: Chloe Stefantsova <cstefantsova@google.com>

tools/spec_parser/Dart.g

@@ -4,6 +4,8 @@
 
 // CHANGES:
 //
+// v0.48 Add support for enhanced parts.
+//
 // v0.47 Make `augment` a built-in identifier (this happened in the feature
 // specification v1.10, but wasn't done here at the time).
 //
@@ -1450,11 +1452,11 @@ libraryExport
     ;
 
 partDirective
-    :    metadata PART uri ';'
+    :    metadata PART configurableUri ';'
     ;
 
 partHeader
-    :    metadata PART OF (dottedIdentifierList | uri)';'
+    :    metadata PART OF uri ';'
     ;
 
 partDeclaration

tools/spec_parser/dart_spec_parser/Dart.g4

@@ -4,6 +4,8 @@
 
 // CHANGES:
 //
+// v0.49 Add support for enhanced parts.
+//
 // v0.48 Make `augment` a built-in identifier (this happened in the feature
 // specification v1.10, but wasn't done here at the time).
 //
@@ -1456,11 +1458,11 @@ libraryExport
     ;
 
 partDirective
-    :    metadata PART uri ';'
+    :    metadata PART configurableUri ';'
     ;
 
 partHeader
-    :    metadata PART OF (dottedIdentifierList | uri)';'
+    :    metadata PART OF uri ';'
     ;
 
 partDeclaration