Update CodeMirror to latest version

[TobiasBg]

From what I can see in the JS file, we are using CodeMirror version 5.29.1 which is over 2 years old, according to ​https://codemirror.net/doc/releases.html

A lot has happened since then, with the current release being 5.49.2.

We should update and set a good example. Getting this in early for 5.4 will allow for testing.

[desrosj]

Thanks for this one, @TobiasBg!

Preferably, #41870 would be fixed before/at the same time as updating CodeMirror so that updating in the future is much easier.

Though that is not a steadfast blocker, if you are interested in this, I recommend looking at how to help out there first.

[davidbaumwald]

This ticket still needs patch and soak time. With 5.4 Beta 1 approaching, this is being moved to Future Release. If any maintainer or committer feels this can be resolved in time or wishes to assume ownership during a specific cycle, feel free to update the milestone accordingly.

[desrosj]

Just noting, the ​current version is now 5.65.9.