refactor(language-service): find expression ASTs using absolute spans (#33387)

Moves to using the absolute span of an expression AST (relative to an
entire template) rather than a relative span (relative to the start
of the expression) to find an expression AST given a position in a
template.

This is part of the changes needed to support text replacement in
templates (#33091).

PR Close #33387

packages/language-service/src/expressions.ts

@@ -18,7 +18,8 @@ function findAstAt(ast: AST, position: number, excludeEmpty: boolean = false): A
   const path: AST[] = [];
   const visitor = new class extends NullAstVisitor {
     visit(ast: AST) {
-      if ((!excludeEmpty || ast.span.start < ast.span.end) && inSpan(position, ast.span)) {
+      if ((!excludeEmpty || ast.sourceSpan.start < ast.sourceSpan.end) &&
+          inSpan(position, ast.sourceSpan)) {
         path.push(ast);
         visitAstChildren(ast, this);
       }