Move pkg/kernel to language version 3.6

This is in preparation for https://dart-review.googlesource.com/c/sdk/+/397164
as packages in a workspace need a recent language version.

Change-Id: If1926192209353fab934efe702391ea10ed3573c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/404581
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Sigurd Meldgaard <[email protected]>

Author: sigurdm

pkg/kernel/lib/testing/type_parser_environment.dart

@@ -217,7 +217,7 @@ class TypeParserEnvironment {
   /* TreeNode | StructuralParameter */ Object lookupDeclaration(String name) {
     Object? result = _declarations[name];
     if (result == null && _parent != null) {
-      return _parent!.lookupDeclaration(name);
+      return _parent.lookupDeclaration(name);
     }
     if (result == null) throw "Not found: $name";
     return result;
@@ -266,7 +266,7 @@ class TypeParserEnvironment {
   /// Use this in subclasses to add support for additional predefined types.
   DartType? getPredefinedNamedType(String name) {
     if (_parent != null) {
-      return _parent!.getPredefinedNamedType(name);
+      return _parent.getPredefinedNamedType(name);
     }
     return null;
   }

pkg/kernel/lib/type_environment.dart

@@ -953,7 +953,7 @@ class StaticTypeContextImpl implements StaticTypeContext {
   @override
   DartType getExpressionType(Expression node) {
     if (_cache != null) {
-      return _cache!.getExpressionType(node, this);
+      return _cache.getExpressionType(node, this);
     } else {
       return node.getStaticTypeInternal(this);
     }
@@ -962,7 +962,7 @@ class StaticTypeContextImpl implements StaticTypeContext {
   @override
   DartType getForInIteratorType(ForInStatement node) {
     if (_cache != null) {
-      return _cache!.getForInIteratorType(node, this);
+      return _cache.getForInIteratorType(node, this);
     } else {
       return node.getIteratorTypeInternal(this);
     }
@@ -971,7 +971,7 @@ class StaticTypeContextImpl implements StaticTypeContext {
   @override
   DartType getForInElementType(ForInStatement node) {
     if (_cache != null) {
-      return _cache!.getForInElementType(node, this);
+      return _cache.getForInElementType(node, this);
     } else {
       return node.getElementTypeInternal(this);
     }

pkg/kernel/pubspec.yaml

@@ -6,7 +6,7 @@ name: kernel
 publish_to: none
 
 environment:
-  sdk: ^3.0.0
+  sdk: ^3.6.0
 
 # Use 'any' constraints here; we get our versions from the DEPS file.
 dependencies: