Handle consecutive spaces when copying and pasting

[luin]

Replaces #4319

Test Plan

1. Paste content contains multiple regular spaces into Quill editor, make sure they are collapsed correctly unless they are inside a <pre>.
2. Paste content contains multiple   spaces into Quill editor, make sure they are not collapsed and they are converted into regular spaces.
3. Copy content that contains multiple spaces from Quill editor, make sure they are copied as non-breaking spaces.
4. Make sure the bug mentioned in Fix white spaces not being preserved when pasted into editor #4319 is not reproducible anymore.