fix(46563): show completions at this type (#46581)

src/compiler/checker.ts

@@ -432,6 +432,7 @@ namespace ts {
             getIndexInfosOfType,
             getSignaturesOfType,
             getIndexTypeOfType: (type, kind) => getIndexTypeOfType(type, kind === IndexKind.String ? stringType : numberType),
+            getIndexType: type => getIndexType(type),
             getBaseTypes,
             getBaseTypeOfLiteralType,
             getWidenedType,
@@ -15344,10 +15345,6 @@ namespace ts {
                 (type.flags & (TypeFlags.InstantiableNonPrimitive | TypeFlags.Index | TypeFlags.TemplateLiteral | TypeFlags.StringMapping) && !isPatternLiteralType(type) ? ObjectFlags.IsGenericIndexType : 0);
         }
 
-        function isThisTypeParameter(type: Type): boolean {
-            return !!(type.flags & TypeFlags.TypeParameter && (type as TypeParameter).isThisType);
-        }
-
         function getSimplifiedType(type: Type, writing: boolean): Type {
             return type.flags & TypeFlags.IndexedAccess ? getSimplifiedIndexedAccessType(type as IndexedAccessType, writing) :
                 type.flags & TypeFlags.Conditional ? getSimplifiedConditionalType(type as ConditionalType, writing) :

src/compiler/types.ts

@@ -4162,6 +4162,7 @@ namespace ts {
         getIndexInfosOfType(type: Type): readonly IndexInfo[];
         getSignaturesOfType(type: Type, kind: SignatureKind): readonly Signature[];
         getIndexTypeOfType(type: Type, kind: IndexKind): Type | undefined;
+        /* @internal */ getIndexType(type: Type): Type;
         getBaseTypes(type: InterfaceType): BaseType[];
         getBaseTypeOfLiteralType(type: Type): Type;
         getWidenedType(type: Type): Type;

src/compiler/utilities.ts

@@ -7414,4 +7414,8 @@ namespace ts {
     export function escapeSnippetText(text: string): string {
         return text.replace(/\$/gm, "\\$");
     }
+
+    export function isThisTypeParameter(type: Type): boolean {
+        return !!(type.flags & TypeFlags.TypeParameter && (type as TypeParameter).isThisType);
+    }
 }