[Proposal] Support copy/paste of rich text into the composer

[horseshoe107]

I have tested the current behaviour of v1.9.2 when copy/pasting from three different sources:

1. An ordinary text editor
2. A Microsoft Word document
3. A webpage

In case 1), since the text editor only contains raw text, it is copied exactly as is to the Wino Mail composer. However 2) and 3) are sources of rich text. Currently pasting text from these sources into the composer loses all formatting - font, modifiers (bold/italic/underline etc), and even carriage returns. The copied text is pasted into Wino Mail as a single line of unformatted text.

Proposal is to support preserving as much of the formatting from rich text sources as possible. Windows Mail generally preserves rich formatting, although it does not seem to be perfect.

As a partial goal, preserving the carriage returns would be most immediately useful.

[Tiktack]

Similar to #309. Those weird behaviors is a result of how Webview2 communicates with UWP app. Cannot be fixed without workarounds.