[BUGFIX] Merge code editor settings properly

The settings for the `typo3-t3editor-codemirror` element were passed in
an `options` attribute, which is unknown. This leads to the issue that
e.g. the `readOnly` flag set in TCA is ignored.

The composed settings are now properly merged.

Resolves: #104084
Releases: main, 12.4
Change-Id: I7e34a8230764c33b7924128176088ab32cb35a58
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84699


Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Andreas Kienast <a.fernandez@scripting-base.de>
Tested-by: Andreas Kienast <a.fernandez@scripting-base.de>