Add Paste Without Formatting to context menu

[cndouglas]

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Fixes #5822

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.

Screenshot:

[cezaraugusto]

++ thanks!!!

[bsclifton]

reverted here:
345233d

original issue reopened:
#5822

Removing milestone from this PR...