Fix 5s lags when using OSC 52 clipboard copy (#20728)

Hilarious repro: `printf "\e]0;A\a\e]52;c;Qg==\a"`

This issue is exactly what happens when you Ctrl+X in a clean file in
msedit and it freezes Windows Terminal. It's because it puts a "•" in
the title and copies the text.

It triggers a title and clipboard change in the same frame which causes
the UI and VT thread to deadlock trying to get the console lock.

.github/actions/spelling/expect/expect.txt

@@ -444,6 +444,7 @@ DELAYLOAD
 DELETEONRELEASE
 depersist
 deprioritized
+DESTROYCLIPBOARD
 devicecode
 Dext
 DFF

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -3624,8 +3624,19 @@ namespace winrt::TerminalApp::implementation
         }
     }
 
-    void TerminalPage::_copyToClipboard(const IInspectable, const WriteToClipboardEventArgs args) const
+    safe_void_coroutine TerminalPage::_copyToClipboard(const IInspectable, const WriteToClipboardEventArgs args) const
     {
+        // This is our hook into SetCopyToClipboardCallback, which gets called by the VT parser thread.
+        // When this gets called, the console lock is being held. This is not a problem per-se, but there
+        // is just a teeny tiny problem... EmptyClipboard() sends WM_DESTROYCLIPBOARD to the previous owner.
+        // *We* may be the previous owner.
+        //
+        // So now we (VT thread, holding the lock) are waiting for us (UI thread, waiting for the lock)
+        // and immediately deadlock. *Tada* 5s app freeze.
+        //
+        // Solution: Just do it on the UI thread. Just like conhost.
+        co_await wil::resume_foreground(Dispatcher());
+
         if (const auto clipboard = clipboard::open(_hostingHwnd.value_or(nullptr)))
         {
             const auto plain = args.Plain();

src/cascadia/TerminalApp/TerminalPage.h

@@ -493,7 +493,7 @@ namespace winrt::TerminalApp::implementation
 
         safe_void_coroutine _SetTaskbarProgressHandler(const IInspectable sender, const IInspectable eventArgs);
 
-        void _copyToClipboard(IInspectable, Microsoft::Terminal::Control::WriteToClipboardEventArgs args) const;
+        safe_void_coroutine _copyToClipboard(IInspectable, Microsoft::Terminal::Control::WriteToClipboardEventArgs args) const;
         void _PasteText();
 
         safe_void_coroutine _ControlNoticeRaisedHandler(const IInspectable sender, const Microsoft::Terminal::Control::NoticeEventArgs eventArgs);