This also fixes a bug introduced accidentally in #153651, whereby the
`JumpTableToSwitch` would convert all the branch weights to 0 except
for one. It didn't trip the test because `update_test_checks` wasn't
run with `-check-globals`. It is now. This also made noticeable that
the direct calls promoted from the indirect call inherited the
`VP`metadata, which should be dropped as it makes no more sense now.
If the indirect call target being recognized as a jump table has profile info, we can accurately synthesize the branch weights of the switch that replaces the indirect call.
Otherwise we insert the "unknown" `MD_prof` to indicate this is the best we can do here.
Part of Issue #147390
Add a pass to convert jump tables to switches.
The new pass replaces an indirect call with a switch + direct calls if all the functions in the jump table are smaller than the provided threshold.
The pass is currently disabled by default and can be enabled by -enable-jump-table-to-switch.
Test plan: ninja check-all
