[cfe] Make VariableDeclaration an abstract interface

The concrete implementation is named `VariableStatement`. The change
is needed as a transition step to the new encoding for variables in
Kernel.

Part of #61572

Change-Id: Ib333f28e9998f2e758a18e4ad4b0a3cf4d642013
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/456620
Reviewed-by: Johnni Winther <[email protected]>
Reviewed-by: Alexander Markov <[email protected]>
Commit-Queue: Chloe Stefantsova <[email protected]>

Author: chloestefantsova

pkg/front_end/lib/src/kernel/internal_ast.dart

@@ -853,7 +853,7 @@ class ReturnStatementImpl extends ReturnStatement {
 }
 
 /// Front end specific implementation of [VariableDeclaration].
-class VariableDeclarationImpl extends VariableDeclaration {
+class VariableDeclarationImpl extends VariableStatement {
   final bool forSyntheticToken;
 
   /// Determine whether the given [VariableDeclarationImpl] had an implicit

pkg/front_end/test/incremental_suite.dart

@@ -2212,7 +2212,7 @@ class Strategy extends EquivalenceStrategy {
   }
 
   @override
-  bool checkVariableDeclaration_binaryOffsetNoTag(
+  bool checkVariableStatement_binaryOffsetNoTag(
     EquivalenceVisitor visitor,
     VariableDeclaration node,
     VariableDeclaration other,

pkg/front_end/test/spell_checking_list_common.txt

@@ -823,6 +823,7 @@ deliberately
 delimited
 delimiter
 delimiters
+deliver
 delta
 demote
 demoted

pkg/front_end/test/testing/suite.dart

@@ -1705,7 +1705,7 @@ class Strategy extends EquivalenceStrategy {
   }
 
   @override
-  bool checkVariableDeclaration_binaryOffsetNoTag(
+  bool checkVariableStatement_binaryOffsetNoTag(
     EquivalenceVisitor visitor,
     VariableDeclaration node,
     VariableDeclaration other,

pkg/front_end/tool/ast_model.dart

@@ -141,7 +141,7 @@ const Map<String?, Map<String, FieldRule?>> _fieldRuleMap = {
   'FunctionType': {'typeParameters': FieldRule(isDeclaration: true)},
   'TypeParameterType': {'parameter': FieldRule(isDeclaration: false)},
   'StructuralParameterType': {'parameter': FieldRule(isDeclaration: false)},
-  'VariableDeclaration': {'_name': FieldRule(name: 'name')},
+  'VariableStatement': {'_name': FieldRule(name: 'name')},
   'AssignedVariablePattern': {'variable': FieldRule(isDeclaration: false)},
   'InvalidPattern': {'declaredVariables': FieldRule(isDeclaration: true)},
   'OrPattern': {'orPatternJointVariables': FieldRule(isDeclaration: false)},