Pasting Heading text from clipboard ads it to a new block

[carladoria]

Steps to reproduce the issue

1. Copy Heading text into your clipboard
2. Paste it to the block in which you're already working

What I expected

I expected the text to be copied inside the block where I was typing

What happened instead

It was copied in a new block as it was recognized as a Heading text

You can see the recording here:

https://drive.google.com/file/d/1vZiaebfqKm10DfKHb0FAbCcKpa_-Pit9/view

[designsimply]

Tested and confirmed that pasting heading text into a paragraph creates a heading. (41s)

I also tested with the classic editor and found that the heading formatting is preserved in the same way in that editor. I believe this is the intended behavior because we cannot always know the intent for every case of pasting formatted content and so the editor preserves the type of formatting of the content that was copied, however, I also saw another discussion noting the following:

If you're pasting the content into a paragraph with content already in it, you most likely want the content in the paragraph I think.

Note: in many applications, you can paste and match style by pressing Option-Shift-Command-V on macOS or Option-Shift-Control-V on Windows or right-click and select "Paste as plain text". This may vary by application. I tested it in a few different browsers macOS 10.13.6 and it worked in my testing.

[maddisondesigns]

This is exactly the reason why I've said we need a Paste as Text button!
#6132

[mtias]

Duplicate of #6555