fix: support all OSC 52 selection types for clipboard sync

[aaradhyaberisfdc]

Problem

The @xterm/addon-clipboard's default BrowserClipboardProvider silently drops OSC 52 clipboard writes for any selection type other than 'c' (system clipboard). See this.

tmux sends selection type 'p' (primary) by default with set-clipboard on, so clipboard never reaches the browser.

The addon's type definitions also have a mismatch (constructor(provider?) in .d.ts vs constructor(base64, provider) at runtime), requiring a @ts-expect-error to pass a custom provider. See this.

Proposed Fix

Replace the default BrowserClipboardProvider with a custom TtydClipboardProvider that accepts all OSC 52 selection types, browsers have a single clipboard with no primary/secondary distinction.

Testing

# All should copy "test" to clipboard
printf '\033]52;c;dGVzdA==\007'   # system clipboard
printf '\033]52;p;dGVzdA==\007'   # primary (tmux default)
printf '\033]52;;dGVzdA==\007'    # empty selection

tmux integration with set -g set-clipboard on and set -g mouse on:

• Mouse drag select in copy-mode copies to system clipboard
• vi copy-mode yank (y) copies to system clipboard

[aaradhyaberisfdc]

@tsl0922 Could I please get a review whenever you get the time?

[tsl0922]

Is it possible to submit it to the upstream?