Add `"branch"` scope type

[pokey]

• Work started in Add "branch" scope type #1149
• See Add keyword for alternatives in a match construct #579 (comment) for discussion

Implementation matrix

	Python	Rust	Java	Typescript	C++	C#
Switch-case	✅	✅	✅	✅
If-else	✅	✅		✅
Try-catch	✅	N/A		✅
Ternary	✅	✅		✅

Implementation specs

Case statements

If-else branches

Try-catch branches

Ternary branches