Immediately sanitize text when pasted

When pasting text, it's sanitized after saving, but not on initial paste. This may result in strange text appearance. This feature request is for text to be sanitized immediately when pasted.

No files or tests are named. Start by locating the editor's paste handling and the existing save-time sanitization, then reproduce the current behavior with pasted text. Done means pasted text is sanitized immediately rather than only after saving.

Written by the indexing model from the issue text.