sendInput should be previewable

[zadjii-msft]

See #9818, 60f63b0, #3121. I literally have this prototyped, just need to check it in. It's important for future issues...

[zadjii-msft]

More cleanly pulled to its own branch: https://github.com/microsoft/terminal/pull/new/dev/migrie/f/12861-preview-input

Note: You'll also want the backspace trimming thing. That merged into TSFControl in 0f32692 but I don't know where its origin was before that.

    void TSFInputControl::ManuallyDisplayText(const winrt::hstring& text)
    {
        _focused = !text.empty();
        Canvas().Visibility(text.empty() ? Visibility::Collapsed : Visibility::Visible);

        _inputBuffer.clear();
        // _editContext.NotifyFocusLeave();
        _activeTextStart = 0;
        _inComposition = false;

        // HACK trim off leading DEL chars.
        std::wstring_view view{ text.c_str() };
        const auto strBegin = view.find_first_not_of(L"\x7f");
        if (strBegin != std::wstring::npos)
        {
            view = view.substr(strBegin * 2);
        }

        TextBlock().Text(winrt::hstring{ view });
        TextBlock().UpdateLayout();
        TryRedrawCanvas();
    }

[DHowett]

Curious how this will handle sendInputd escape sequences!

[zadjii-msft]

Protip, revert 7c3fd2a

I backed it out because it:

• worked wacky with wide glyphs / unicode surrogates and the backspacing code
• the backspacing code was hacky kinda always
• it didn't always scale and offset to the correct position
• didn't really handle line wrapping well
• with the pwsh ghost text, was very confusing

---

you may also need 8f0b6f8

[zadjii-msft]

Punting out of 1.19. This was wacky as-is. We may want to come back to re-try this with more runway.