Colocate buffer types in buffer/Types.ts

The import/no-cycle refactor had moved IBuffer, IBufferSet, and related
cell/line types into src/common/Types.ts, with buffer/Types.ts only
re-exporting them. That inverted the natural module boundary and made
buffer code depend on the top-level types hub.

Define buffer-owned types in buffer/Types.ts instead:
- CharData, IExtendedAttrs, IAttributeData, ICellData, IBufferLine
- IMarker, IBuffer, IBufferSet, BufferIndex

Restore UnderlineStyle to buffer/Constants.ts (used by IExtendedAttrs)
and remove those definitions from Types.ts.

buffer/Types.ts imports only what it needs from outside the buffer layer:
ICircularList and ICharset from Types, IDisposable from Lifecycle,
IEvent from Event, and UnderlineStyle from Constants. Types.ts does not
import buffer/Types.ts, so the previous Types <-> buffer cycle stays broken.

Update imports across common, browser, headless, addons, and tests to use
common/buffer/Types for buffer types rather than common/Types.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/common/CoreTerminal.ts

@@ -26,7 +26,8 @@ import { InstantiationService } from './services/InstantiationService';
 import { LogService } from './services/LogService';
 import { BufferService, BufferServiceConstants } from './services/BufferService';
 import { OptionsService } from './services/OptionsService';
-import { IDisposable, IAttributeData, IScrollEvent, ITerminalOptions, IParams } from './Types';
+import { IDisposable, IScrollEvent, ITerminalOptions, IParams } from './Types';
+import { IAttributeData, IBufferSet } from './buffer/Types';
 import { CoreService } from './services/CoreService';
 import { MouseStateService } from './services/MouseStateService';
 import { UnicodeV6 } from './input/UnicodeV6';
@@ -34,7 +35,6 @@ import { UnicodeService } from './services/UnicodeService';
 import { CharsetService } from './services/CharsetService';
 import { updateWindowsModeWrappedState } from './WindowsMode';
 import { IFunctionIdentifier } from './parser/Types';
-import { IBufferSet } from './buffer/Types';
 import { InputHandler } from './InputHandler';
 import { WriteBuffer } from './input/WriteBuffer';
 import { OscLinkService } from './services/OscLinkService';