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>

src/browser/OscLinkProvider.test.ts

@@ -4,11 +4,11 @@
  */
 
 import { assert } from 'chai';
-import { OscLinkProvider } from 'browser/OscLinkProvider';
-import { ILink } from 'browser/Types';
-import { createCellData, MockBufferService, MockOptionsService } from 'common/TestUtils.test';
-import { IBufferService, IOscLinkService } from 'common/services/Services';
-import { IBufferLine, IOscLinkData } from 'common/Types';
+import { OscLinkProvider } from './OscLinkProvider';
+import { ILink } from './Types';
+import { createCellData, MockBufferService, MockOptionsService } from '../common/TestUtils.test';
+import { IBufferService, IOscLinkService } from '../common/services/Services';
+import { IBufferLine, IOscLinkData } from '../common/Types';
 
 class TestOscLinkService implements IOscLinkService {
   public serviceBrand: any;