This change produces the debug info for interpreted byte code.

Changes:

On the compiler:

1. Changes the offset allocator so that variable are all associated with the first and last instruction when it is alive, and all instructions associated with the nativeOffset, so we have the liveness of all variables and the nativeOffset for all instruction.
2. Report, for all 1st instruction that has an IL offset, to the debugger a mapping between its ILOffset and IROffset
3. Report, for all IL variables, their liveness and their offset from the virtualized stack pointer.

On the stack walker:

1. Whenever we set SP to pFrame, we also set FP to pFrame->pStack, that is because the offset of the variables are relative to pFrame->pStack, and so the debugger needs to know about it, and we chose to report that value through the FP.

On the debugger:

1. It turns out REGNUM_FP is not defined for AMD64 and is causing problem, just define it there.

The change is tested under SOS so that if we set a breakpoint inside the interpreter routine and do a !clrstack -i -a, we will be able to see the argument and local variables values.

@janvorli
@BrzVlad
@kg
@dotnet/dotnet-diag