Allow locking of the draw mode

[quincylvania]

When adding many features of the same type, it becomes unnecessarily repetitive to keep selecting the draw mode (point, line, or area). There should be a mechanism to lock into a mode so it stays active even after adding a feature. Double-clicking would be a simple way to lock, with a single click sufficient to unlock.

This would be especially powerful combined with #5873 since then users could quickly add many features of the same type with no clicks required in-between additions.

While theoretically this would make it easier to accidentally add many untagged features, #5830 will prevent their upload and help users tag or remove them.

Draw mode buttons with quick presets after #5873:

With single feature draw mode active (on click or hotkey):

Possible UI with locked draw mode active (on double click):

[quincylvania]

I'm working on this today, targeting a "Repeat" toolbar button that appears during adding/drawing.

[quincylvania]

I did this. Get ready for speed!

🏎💨💨💨

[sun-geo]

:-)