Move common primitives to src/common/primitives/

Phase 1 of #5963: reorganize building blocks (buffer, parser, input,
data, and shared utilities) under common/primitives/. Runtime code
(services, public API, CoreTerminal, InputHandler) stays in place.

Update import paths across browser, headless, addons, and tests.
Add TypeScript path mappings so common/* aliases resolve primitives
first, then the common root.

Co-authored-by: Daniel Imms <Tyriar@users.noreply.github.com>

addons/addon-progress/src/ProgressAddon.ts

@@ -5,7 +5,7 @@
 
 import type { Terminal, ITerminalAddon, IDisposable } from '@xterm/xterm';
 import type { ProgressAddon as IProgressApi, IProgressState } from '@xterm/addon-progress';
-import type { Emitter, IEvent } from 'common/Event';
+import type { Emitter, IEvent } from 'common/primitives/Event';
 
 
 const enum ProgressType {

addons/addon-progress/src/tsconfig.json

@@ -16,6 +16,7 @@
     ],
     "paths": {
       "common/*": [
+        "../../../src/common/primitives/*",
         "../../../src/common/*"
       ],
       "browser/*": [