langs: unused imports in generated src/index.ts (e.g. objectiveC)

[EurFelux]

Problem

The generated extensions/langs/src/index.ts contains unused imports. For example:

import { csharp, dart, kotlin, objectiveC, objectiveCpp, scala, squirrel } from '@codemirror/legacy-modes/mode/clike';

objectiveC is imported but never referenced in the langs map — only objectiveCpp is used (for the .mm extension).

Root Cause

In gen-langs-map.cjs, parseLoadSpec() calls addNamed() as a side effect during AST parsing, which adds symbols to the import list immediately. Later, when multiple languages share the same file extension (e.g. Objective-C and Octave both use .m), the dedup step (mapObj.set(k, v) — last one wins) drops the losing entry's expression from the output, but the import was already registered and persists.

Impact

• Minor: unused imports bloat the generated file and may trigger linter warnings
• No runtime breakage — the unused symbols are simply dead code

Potential Fix

Defer addNamed calls until after the dedup step, so only symbols actually referenced in the final langs map get imported. This would require restructuring the generation flow to separate "parse specs" from "collect imports".

Related: #760