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>

addons/addon-webgl/src/CharAtlasUtils.test.ts

@@ -6,8 +6,8 @@
 import { assert } from 'chai';
 import { configEquals } from './CharAtlasUtils';
 import { ICharAtlasConfig } from './Types';
-import { NULL_COLOR } from 'common/Color';
-import { IColor } from 'common/Types';
+import { NULL_COLOR } from '../../../src/common/Color';
+import { IColor } from '../../../src/common/Types';
 
 function createTestConfig(overrides: Partial<ICharAtlasConfig> = {}): ICharAtlasConfig {
   const color: IColor = { css: '#ffffff', rgba: 0xffffffff };