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>

src/common/Types.ts

@@ -4,7 +4,7 @@
  */
 
 import { IFunctionIdentifier, ITerminalOptions as IPublicTerminalOptions } from '@xterm/xterm';
-import type { IEvent } from './Event';
+import type { IEvent } from './primitives/Event';
 
 /** sequence params serialized to js arrays */
 export type ParamsArray = (number | number[])[];