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/scrollable/abstractScrollbar.ts

@@ -11,7 +11,7 @@ import { ScrollbarArrow, IScrollbarArrowOptions } from './scrollbarArrow';
 import { ScrollbarState } from './scrollbarState';
 import { ScrollbarVisibilityController } from './scrollbarVisibilityController';
 import { Widget } from './widget';
-import * as platform from 'common/Platform';
+import * as platform from '../../common/Platform';
 import { INewScrollPosition, Scrollable, ScrollbarVisibility } from './scrollable';
 
 /**