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/InputHandler.ts

@@ -4,7 +4,8 @@
  * @license MIT
  */
 
-import { IInputHandler, IAttributeData, IDisposable, IWindowOptions, IColorEvent, IParseStack, ColorIndex, ColorRequestType, SpecialColorIndex } from './Types';
+import { IInputHandler, IDisposable, IWindowOptions, IColorEvent, IParseStack, ColorIndex, ColorRequestType, SpecialColorIndex } from './Types';
+import { IAttributeData, IBuffer } from './buffer/Types';
 import { C0, C1 } from './data/EscapeSequences';
 import { CHARSETS, DEFAULT_CHARSET } from './data/Charsets';
 import { EscapeSequenceParser } from './parser/EscapeSequenceParser';
@@ -20,7 +21,6 @@ import { UnicodeService } from './services/UnicodeService';
 import { OscHandler } from './parser/OscParser';
 import { DcsHandler } from './parser/DcsParser';
 import { ApcHandler } from './parser/ApcParser';
-import { IBuffer } from './buffer/Types';
 import { parseColor } from './input/XParseColor';
 import { Emitter } from './Event';
 import { XTERM_VERSION } from './Version';