[mbr] Add a global has_updates flag

[lambdageek]

Use it to take the slow path in metadata lookups when there's at least one delta applied.

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Issue Details

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Use it to take the slow path in metadata lookups when there's at least one delta applied.

Author:	lambdageek
Assignees:	-
Labels:	area-VM-meta-mono
Milestone:	-

[lambdageek]

This is in part motivated by #46842 perf results, and in part by some future changes that will affect the effective table lookup.

I was able to identify some differences in profiles, primarily due to profiler choices around mono_metadata_decode_row and mono_metadata_decode_row_col. I added #47716, but it doesn't not alter the run times in any meaningful way. (it does nudge the xcode clang inliner to the same choices as before, so the profile stack traces look more similar, and I think it's better to logically separate the slow path with an explicit state change.)