Enable stress testing for fragmented unwind

[AndyAyersMS]

We should create a stress mode (or mixin for jit stress) where the jit intentionally produces fragmented unwind even for small methods (for arm/arm64).

This can leverage COMPlus_JitSplitFunctionSize.

See commentary over in #10800.

cc @BruceForstall @dotnet/jit-contrib

category:implementation
theme:testing
skill-level:intermediate
cost:medium

[BruceForstall]

Moving out of 3.0.

Some WIP here: dotnet/coreclr#23233

It would be be easier if we first fixed https://github.com/dotnet/coreclr/issues/23365 and https://github.com/dotnet/coreclr/issues/23364