Make the scope bag an object instead of an array

Now that the scope bag is a `Record<string, unknown>`, the lexical symbol
names are always carried alongside their values. This eliminates the need
for the `lexicalSymbols` slot in the wire format block (previously only
available when `debugSymbols` was enabled) and allows `meta()` to derive
`lexical` names and `scopeValues` directly from the scope object's keys
and values.

See also: upstream PR #21224, PR #21068.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Author: NullVoxPopuli

packages/@glimmer/compiler/lib/compiler.ts

@@ -123,9 +123,8 @@ export function precompile(
 ): TemplateJavascript {
   const [block, usedLocals] = precompileJSON(source, options);
 
-  if ('emit' in options && options.emit?.debugSymbols && usedLocals.length > 0) {
-    block.push(usedLocals);
-  }
+  // lexical symbol names are now carried by the scope object itself (as keys),
+  // so we no longer need to push them into the wire format block for debug symbols.
 
   const moduleName = options.meta?.moduleName;
   const idFn = options.id || defaultId;

packages/@glimmer/interfaces/lib/compile/wire-format/api.d.ts

@@ -373,7 +373,6 @@ export type SerializedTemplateBlock = [
   statements: Statements.Statement[],
   locals: string[],
   upvars: string[],
-  lexicalSymbols?: string[],
 ];
 
 /**