docs(common): correct ST sequence metadata and comment typos

- EscapeSequenceParser: ESC ST is ESC backslash (0x1B 0x5C), not ESC
  plus a double-quote character; align @vt metadata with C1 ST on the
  following line.
- Color.contrastRatio: document l2 as the second luminance argument.
- Marker.dispose: fix "change" -> "chance" in dispose listener comment.
- Buffer.clear: fix possessive "it's" -> "its" in JSDoc.

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

src/common/buffer/Buffer.ts

@@ -142,7 +142,7 @@ export class Buffer extends Disposable implements IBuffer {
   }
 
   /**
-   * Clears the buffer to it's initial state, discarding all previous data.
+   * Clears the buffer to its initial state, discarding all previous data.
    */
   public clear(): void {
     this._stringCache.clear();

src/common/buffer/Marker.ts

@@ -30,7 +30,7 @@ export class Marker implements IMarker {
     }
     this.isDisposed = true;
     this.line = -1;
-    // Emit before super.dispose such that dispose listeners get a change to react
+    // Emit before super.dispose such that dispose listeners get a chance to react
     this._onDispose.fire();
     dispose(this._disposables);
     this._disposables.length = 0;