Consolidate fragment writing into _writeTemplateFragment.

Migrate hand-rolled _writeXxxFragment helpers to the shared _writeTemplateFragment. This eliminates duplicated serialization logic  (ID / name / offset / modifiers), shrinks the code base, and makes it easier to add new fragment types without boiler-plate.

Removed flags from `bundle_reader` and `bundle_writer`, will remove flag classes in the future as they will be replaced with reading/writing modifiers.

Change-Id: I79aabd1e94bfa831d6718bb2889a6a00e6561112
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/437102
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Paul Berry <[email protected]>
Reviewed-by: Paul Berry <[email protected]>

Author: fshcheglov

pkg/analyzer/lib/src/dart/analysis/driver.dart

@@ -110,7 +110,7 @@ testFineAfterLibraryAnalyzerHook;
 // TODO(scheglov): Clean up the list of implicitly analyzed files.
 class AnalysisDriver {
   /// The version of data format, should be incremented on every format change.
-  static const int DATA_VERSION = 481;
+  static const int DATA_VERSION = 482;
 
   /// The number of exception contexts allowed to write. Once this field is
   /// zero, we stop writing any new exception contexts in this process.

pkg/analyzer/lib/src/summary2/bundle_reader.dart

@@ -311,7 +311,7 @@ class LibraryReader {
       return _readTemplateFragment(
         create: (name) {
           var fragment = ClassFragmentImpl(name2: name, nameOffset: -1);
-          ClassElementFlags.read(_reader, fragment);
+          fragment.readModifiers(_reader);
           fragment.typeParameters = _readTypeParameters();
 
           _lazyRead((membersOffset) {
@@ -518,7 +518,7 @@ class LibraryReader {
       return _readTemplateFragment(
         create: (name) {
           var fragment = EnumFragmentImpl(name2: name, nameOffset: -1);
-          EnumElementFlags.read(_reader, fragment);
+          fragment.readModifiers(_reader);
           fragment.typeParameters = _readTypeParameters();
 
           // TODO(scheglov): consider reading lazily
@@ -604,7 +604,7 @@ class LibraryReader {
       return _readTemplateFragment(
         create: (name) {
           var fragment = ExtensionFragmentImpl(name2: name, nameOffset: -1);
-          ExtensionElementFlags.read(_reader, fragment);
+          fragment.readModifiers(_reader);
           fragment.typeParameters = _readTypeParameters();
           _readFieldFragments(fragment);
           fragment.getters = _readGetterFragments();
@@ -658,7 +658,9 @@ class LibraryReader {
       return _readTemplateFragment(
         create: (name) {
           var fragment = ExtensionTypeFragmentImpl(name2: name, nameOffset: -1);
-          ExtensionTypeElementFlags.read(_reader, fragment);
+          fragment.readModifiers(_reader);
+          fragment.hasRepresentationSelfReference = _reader.readBool();
+          fragment.hasImplementsSelfReference = _reader.readBool();
           fragment.typeParameters = _readTypeParameters();
 
           // TODO(scheglov): consider reading lazily
@@ -997,7 +999,7 @@ class LibraryReader {
       return _readTemplateFragment(
         create: (name) {
           var fragment = MixinFragmentImpl(name2: name, nameOffset: -1);
-          MixinElementFlags.read(_reader, fragment);
+          fragment.readModifiers(_reader);
           fragment.superInvokedNames = _reader.readStringReferenceList();
           fragment.typeParameters = _readTypeParameters();