Remove TypeScript path mappings in favor of relative imports

Fixes https://github.com/xtermjs/xterm.js/issues/5896

TypeScript path mappings for common/*, browser/*, and headless/*
were not rewritten in emitted JavaScript, which forced webpack resolve
aliases and NODE_PATH workarounds so runtime could resolve modules.
That added build complexity and broke tooling such as ESLint import/no-cycle.

Changes:
- Convert ~750 imports across src/, addons/, and test/ to relative paths
- Remove common/browser/headless paths and src catch-all mappings from tsconfigs
  (keep @xterm/addon-* demo and addon typings paths)
- Remove webpack resolve.alias for common, browser, headless, and vs
- Drop NODE_PATH from unit tests, benchmarks, and VS Code launch config
- Fix addon-image IIPImageStorage to import ./Types after removing catch-all *

Verified: npm run build, esbuild, package, package-headless
Co-authored-by: Cursor <cursoragent@cursor.com>

webpack.config.headless.js

@@ -8,8 +8,7 @@ const path = require('path');
 /**
  * This webpack config does a production build for xterm.js headless. It works by taking the output
  * from tsc (via `npm run watch` or `npm run prebuild`) which are put into `out/` and webpacks them
- * into a production mode umd library module in `lib-headless/`. The aliases are used fix up the
- * absolute paths output by tsc (because of `baseUrl` and `paths` in `tsconfig.json`.
+ * into a production mode umd library module in `lib-headless/`.
  *
  * @type {import('webpack').Configuration}
  */
@@ -29,11 +28,6 @@ const config = {
   resolve: {
     modules: ['./node_modules'],
     extensions: [ '.js' ],
-    alias: {
-      common: path.resolve('./out/common'),
-      headless: path.resolve('./out/headless'),
-      vs: path.resolve('./out/vs')
-    }
   },
   output: {
     filename: 'xterm-headless.js',