JIT: implement type checker

[AndyAyersMS]

There are a couple categories of issues in the JIT IR that could have been caught earlier if we ran some kind of type checking phase:

• unexpected appearance of short integer types (Tests under: BasicEventSourceTests.TestsWrite failed with "System.Reflection.MissingMetadataException" #22666)
• mismatched uses of byrefs/native ints ([Security] Use safe integer arithmetic for memory allocation #19257)
• TYP_UINT and TYP_ULONG are invalid on nodes

We might also want to restructure the early part of the jit so we can run checks sooner...

category:implementation
theme:ir
skill-level:expert
cost:extra-large

[mikedn]

We might also want to restructure the early part of the jit so we can run checks sooner...

What exactly do you have in mind?

[AndyAyersMS]

Thinks like adopting Phases everywhere so there's common place to hang begin/end activities like dumping and checking and such.