[mono] Allow CustomAttribute table modifications if Parent stays unchanged #55097

Allow nullability analysis of modified method bodies.

Roslyn emits nullability attributes by emitting an update to a CustomAttribute table row when a method body is updated.
In most(all?) cases the Constructor stays the same too. The value might or might not change, but we don't care.

This is distinct from supporting full custom attribute changes. In this case Roslyn doesn't consider a CA row update as a rude edit even with just Baseline capabilities.

(Previously Roslyn used to emit new CA rows when a method body was updated. Mono ignored it because we tacitly allow through many row additions to most tables. Modifications we scrutinize.)

After this is fixed the ApplyUpdateTest and the hot reload functional tests can be updated to re-enable Nullability analysis for the modifiable assembly projects.

Contributes to #44806