This commit implements most features needed for simple text editing.
Active text strip can be edited in preview by pressing tab key, which
enabled text editing mode. With this mode active, outline matches text
boundary box and cursor is drawn.
Cursor can be moved with usual keys. Pressing shift starts selection.
Selection and navigation works when text is scaled or rotated. Mirrored
text is not supported in this PR. it can be done, but the text is
unreadable that way, so I kept it simple.
Multi line text is supported. Pressing return key starts new line.
Copy/paste operator uses OS copy paste buffer, so text from other apps
can be pasted.
Text is still limited to 512 characters. Text string property still
exists in side panel and is limited to single line. Individual
characters can not be styled in different way like in 3D viewport, but
the code is mostly ready for such feature.
Ref: #126547
Pull Request: https://projects.blender.org/blender/blender/pulls/127239
8ce5356522