feat(compiler): Propagate source span and value span to Variable AST (#36047)

This commit propagates the `sourceSpan` and `valueSpan` of a `VariableBinding`
in a microsyntax expression to `ParsedVariable`, and subsequently to
View Engine Variable AST and Ivy Variable AST.

Note that this commit does not propagate the `keySpan`, because it involves
significant changes to the template AST.

PR Close #36047

packages/compiler/src/expression_parser/ast.ts

@@ -743,8 +743,14 @@ export class ParsedEvent {
       public handlerSpan: ParseSourceSpan) {}
 }
 
+/**
+ * ParsedVariable represents a variable declaration in a microsyntax expression.
+ */
 export class ParsedVariable {
-  constructor(public name: string, public value: string, public sourceSpan: ParseSourceSpan) {}
+  constructor(
+      public readonly name: string, public readonly value: string,
+      public readonly sourceSpan: ParseSourceSpan, public readonly keySpan: ParseSourceSpan,
+      public readonly valueSpan?: ParseSourceSpan) {}
 }
 
 export const enum BindingType {