Add JitStress mode that forces a particular mechanism of stack probing - helper or inlined code

[echesakov]

A decision on what mechanism ("JIT helper" or "inlined code") is used for stack probing depends purely on a method frame size and the getVeryLargeFrameSize() value for target platform. Given that most of the methods have smaller frame sizes, the "JIT helper" mechanism might not have enough test coverage in the CI.

The proposal is to introduce a JitStress mode that would force a particular mechanism of stack probing without taking into account a method frame size. In theory, both should work for some range of frame size values. The "inlined code" might be restricted by number of instructions allowed in a function prolog and, on linux-x64, by the maximum distance below rsp that can be safely probed without causing an app to be terminated.

@dotnet/jit-contrib

category:testing
theme:stack-allocation

[echesakov]

Un-assigning myself
cc @BruceForstall