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/buffer/Buffer.test.ts

@@ -4,13 +4,13 @@
  */
 
 import { assert } from 'chai';
-import { Buffer } from 'common/buffer/Buffer';
-import { CircularList } from 'common/CircularList';
-import { MockOptionsService, MockBufferService, MockLogService, createCellData } from 'common/TestUtils.test';
-import { BufferLine, DEFAULT_ATTR_DATA } from 'common/buffer/BufferLine';
-import { BufferLineStringCache } from 'common/buffer/BufferLineStringCache';
-import { CellData } from 'common/buffer/CellData';
-import { ExtendedAttrs } from 'common/buffer/AttributeData';
+import { Buffer } from './Buffer';
+import { CircularList } from '../CircularList';
+import { MockOptionsService, MockBufferService, MockLogService, createCellData } from '../TestUtils.test';
+import { BufferLine, DEFAULT_ATTR_DATA } from './BufferLine';
+import { BufferLineStringCache } from './BufferLineStringCache';
+import { CellData } from './CellData';
+import { ExtendedAttrs } from './AttributeData';
 
 const INIT_COLS = 80;
 const INIT_ROWS = 24;