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/common/services/DecorationService.test.ts

@@ -5,12 +5,12 @@
 
 import { assert } from 'chai';
 import { DecorationLineCache, DecorationService } from './DecorationService';
-import { IMarker } from 'common/Types';
-import { Disposable } from 'common/Lifecycle';
-import { Emitter } from 'common/Event';
-import { MockLogService, MockBufferService, MockOptionsService } from 'common/TestUtils.test';
-import { Buffer } from 'common/buffer/Buffer';
-import { DEFAULT_ATTR_DATA } from 'common/buffer/BufferLine';
+import { IMarker } from '../Types';
+import { Disposable } from '../Lifecycle';
+import { Emitter } from '../Event';
+import { MockLogService, MockBufferService, MockOptionsService } from '../TestUtils.test';
+import { Buffer } from '../buffer/Buffer';
+import { DEFAULT_ATTR_DATA } from '../buffer/BufferLine';
 
 function createFakeMarker(line: number): IMarker {
   return Object.freeze(new class extends Disposable {