Increase fraction of code executed by tier 2.

[markshannon]

According to stats and profiling only about 40% of bytecode instructions are executed by tier 2 and the remaining 60% by tier 1.

We the expected improvements to the JIT and tier 2 optimizer we expect tier 2 (with JIT) to have a significantly faster than tier 1.
It therefore make sense to get the fraction of instructions executed by tier 2 up from 40% to nearer 90%.

To do that we need to:

• Enter tier 2 at some function entry points as well as back edges. #118094
• Stay in tier 2 when exiting executors in most cases Trace stitching #112354
• Increase the number of micro-ops that we can handle in tier 2 #118095