fix(language-service): get quick info at local var location to align with TS semantics and support type narrowing

Previously, the Language Service fetched Quick Info and definitions for template variables (such as `@let` declarations) using mapping to their `initializerLocation` (the right-hand side expression). This aggressively bubbled the type, JSDoc, and definition identity of the initializer backwards onto the variable itself.

This approach had two flaws:
1. It broke type narrowing because the LS read the original un-narrowed type from the source expression rather than the type of the narrowed intermediate variable in the Type Check Block.
2. It deviated from native TypeScript semantics, where a local `let` binding (`let address = hero.address`) does not inherit the docstrings or `(property)` kind of its initializer, acting solely as a local inferred variable.

By using `localVarLocation` rather than `initializerLocation` for LetDeclaration Quick Info and Type Definitions, these intermediate variables now properly preserve type narrowing within templates and flawlessly match the standard behavior expected of TypeScript block variables. `VariableSymbol.initializerLocation` is retained solely to map the value spans of structural directive contexts (e.g., `exportAs` strings).

fixes #65491

packages/compiler-cli/src/ngtsc/typecheck/api/symbols.ts

@@ -274,11 +274,6 @@ export interface LetDeclarationSymbol {
    * The location in the shim file for the identifier of the `@let` declaration.
    */
   localVarLocation: TcbLocation;
-
-  /**
-   * The location in the shim file of the `@let` declaration's initializer expression.
-   */
-  initializerLocation: TcbLocation;
 }
 
 /**

packages/compiler-cli/src/ngtsc/typecheck/src/template_symbol_builder.ts

@@ -646,9 +646,9 @@ export class SymbolBuilder {
     return {
       tsType: nodeValueSymbol.tsType,
       tsSymbol: nodeValueSymbol.tsSymbol,
-      initializerLocation: nodeValueSymbol.tcbLocation,
       kind: SymbolKind.Variable,
       declaration: variable,
+      initializerLocation: nodeValueSymbol.tcbLocation,
       localVarLocation: {
         tcbPath: this.tcbPath,
         isShimFile: this.tcbIsShim,
@@ -727,7 +727,7 @@ export class SymbolBuilder {
       return null;
     }
 
-    const nodeValueSymbol = this.getSymbolOfTsNode(node.initializer!);
+    const nodeValueSymbol = this.getSymbolOfTsNode(node.name);
 
     if (nodeValueSymbol === null) {
       return null;
@@ -736,7 +736,6 @@ export class SymbolBuilder {
     return {
       tsType: nodeValueSymbol.tsType,
       tsSymbol: nodeValueSymbol.tsSymbol,
-      initializerLocation: nodeValueSymbol.tcbLocation,
       kind: SymbolKind.LetDeclaration,
       declaration: decl,
       localVarLocation: {

packages/compiler-cli/src/ngtsc/typecheck/test/type_checker__get_symbol_of_template_node_spec.ts

@@ -201,12 +201,6 @@ runInEachFileSystem(() => {
           assertVariableSymbol(symbol);
           expect(program.getTypeChecker().typeToString(symbol.tsType!)).toEqual('any');
           expect(symbol.declaration.name).toEqual('contextFoo');
-
-          // Ensure we can map the shim locations back to the template
-          const initializerMapping = templateTypeChecker.getSourceMappingAtTcbLocation(
-            symbol.initializerLocation,
-          )!;
-          expect(initializerMapping.span.toString()).toEqual('bar');
           const localVarMapping = templateTypeChecker.getSourceMappingAtTcbLocation(
             symbol.localVarLocation,
           )!;
@@ -2025,11 +2019,6 @@ runInEachFileSystem(() => {
         expect(program.getTypeChecker().typeToString(symbol.tsType!)).toEqual('string');
         expect(symbol.declaration.name).toEqual('message');
 
-        // Ensure we can map the shim locations back to the template
-        const initializerMapping = templateTypeChecker.getSourceMappingAtTcbLocation(
-          symbol.initializerLocation,
-        )!;
-        expect(initializerMapping.span.toString()).toEqual(`'The value is ' + value`);
         const localVarMapping = templateTypeChecker.getSourceMappingAtTcbLocation(
           symbol.localVarLocation,
         )!;