Tab feature conflicts: need a single, predictable priority order

[Testudinidae]

Description

Our Tab-related features overlap and create unpredictable behavior when enabled together:

• Insert spaces
• Key trigger
• Matrix shortcut
• Tabout

When multiple cursors or selections are involved, the result is even less predictable. We need one unified priority order and consistent rules for single cursor, multi-cursor, and selection cases.

Importance

Predictable Tab = fewer surprises, easier to use.

[superle3]

#443 somewhat avoids the issue by making them configurable. But with a single cursor it probably should be (snippet trigger) > (tabout enclosed by a brace) > (matrix shortcut) > (tabout not enclosed by brace) > indenting (tabout currently does both at priority less the matrix shortcuts).

With selections indent makes the most sense but with multicursor where some could have selections, idk. Don't use multicursor a lot, so I don't know what's most intuitive.