bug#71404: 30.0.50; [WISHLIST] string-edit-mode should allow changing major mode

[Nicholas Vollmer]

Nicholas Vollmer <nv@parenthetic.dev> writes:

Attached is a proof-of-concept patch which addresses bugs #71404, 
#71405, and #71406 
I'll take care of that if/when the design is agreed upon.

The patch rewrites string-edit-mode as a minor mode.
It utilizes an overlay for the edit prompt (to persist across 
major mode changes) and prevents the prompt separator from being 
deleted.
It persists the buffer-local editing data so that the major mode 
can be changed and the edit can still be completed.
It uses #'ignore as the default abort function if none is 
provided.