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/buffer/Buffer.ts

@@ -6,7 +6,8 @@
 import { CircularList, IInsertEvent } from '../CircularList';
 import { Disposable, toDisposable } from '../Lifecycle';
 import { IdleTaskQueue } from '../TaskQueue';
-import { IAttributeData, IBufferLine, ICellData, ICharset } from '../Types';
+import { ICharset } from '../Types';
+import { IAttributeData, IBuffer, IBufferLine, ICellData } from './Types';
 import { ExtendedAttrs } from './AttributeData';
 import { BufferLine, DEFAULT_ATTR_DATA } from './BufferLine';
 import { BufferLineStringCache } from './BufferLineStringCache';
@@ -14,7 +15,6 @@ import { getWrappedLineTrimmedLength, reflowLargerApplyNewLayout, reflowLargerCr
 import { CellData } from './CellData';
 import { NULL_CELL_CHAR, NULL_CELL_CODE, NULL_CELL_WIDTH, WHITESPACE_CELL_CHAR, WHITESPACE_CELL_CODE, WHITESPACE_CELL_WIDTH } from './Constants';
 import { Marker } from './Marker';
-import { IBuffer } from './Types';
 import { DEFAULT_CHARSET } from '../data/Charsets';
 import { IBufferService, ILogService, IOptionsService } from '../services/Services';