Provide paste as plain text feature in right click context menu

[srirambv]

From support

It would be nice to have "paste as plain text" as a right-click option when filling in forms.

+1 from me as well

[cndouglas]

See PR #6126.

[bsclifton]

Reopening after issue discovered #6268 (comment) and revert was done with 345233d

We'll want to make sure the proper fix doesn't affect URL bar 😄

[cndouglas]

New PR: #6359

[bsclifton]

Fixed with #6359 which was merged into branch 0.13.1-branch.

Test Plan:

1. Open a new Brave tab and navigate to a site with an input field (preferably a field that accepts rich text).
2. Open your favorite rich text editor (e.g. TextEdit).
3. Type a string of text and give the text some formatting (e.g. bold).
4. Switch back to Brave. Right click the input field.
5. Click Paste Without Formatting.
6. Make sure the pasted text has no formatting.