Add a FormalParameter.isExplicitlyTyped getter.

This is needed for my work on
dart-lang/language#731 (improved inference
for fold etc.) because I want to use slightly different heuristics
when the closure passed to `fold` has explicitly parameter types.

Change-Id: I7567df620e22bb53fcdb0f5cd8ceadf0c58c2126
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/240504
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

Author: stereotype441

pkg/analyzer/lib/dart/ast/ast.dart

@@ -2070,6 +2070,9 @@ abstract class FormalParameter implements AstNode {
   /// Return `true` if this parameter was declared with the 'const' modifier.
   bool get isConst;
 
+  /// Indicates whether the parameter has an explicit type.
+  bool get isExplicitlyTyped;
+
   /// Return `true` if this parameter was declared with the 'final' modifier.
   ///
   /// Parameters that are declared with the 'const' modifier will return

pkg/analyzer/lib/src/dart/ast/ast.dart

@@ -3126,6 +3126,9 @@ class DefaultFormalParameterImpl extends FormalParameterImpl
   @override
   bool get isConst => _parameter.isConst;
 
+  @override
+  bool get isExplicitlyTyped => _parameter.isExplicitlyTyped;
+
   @override
   bool get isFinal => _parameter.isFinal;
 
@@ -4437,6 +4440,9 @@ class FieldFormalParameterImpl extends NormalFormalParameterImpl
   @override
   bool get isConst => keyword?.keyword == Keyword.CONST;
 
+  @override
+  bool get isExplicitlyTyped => _parameters != null || _type != null;
+
   @override
   bool get isFinal => keyword?.keyword == Keyword.FINAL;
 
@@ -5633,6 +5639,9 @@ class FunctionTypedFormalParameterImpl extends NormalFormalParameterImpl
   @override
   bool get isConst => false;
 
+  @override
+  bool get isExplicitlyTyped => true;
+
   @override
   bool get isFinal => false;
 
@@ -9523,6 +9532,9 @@ class SimpleFormalParameterImpl extends NormalFormalParameterImpl
   @override
   bool get isConst => keyword?.keyword == Keyword.CONST;
 
+  @override
+  bool get isExplicitlyTyped => _type != null;
+
   @override
   bool get isFinal => keyword?.keyword == Keyword.FINAL;
 
@@ -10348,6 +10360,9 @@ class SuperFormalParameterImpl extends NormalFormalParameterImpl
   @override
   bool get isConst => keyword?.keyword == Keyword.CONST;
 
+  @override
+  bool get isExplicitlyTyped => _parameters != null || _type != null;
+
   @override
   bool get isFinal => keyword?.keyword == Keyword.FINAL;