[NFC][InstCombine] PHI-aware aggregate reconstruction: don't capture UseBB in...

[NFC][InstCombine] PHI-aware aggregate reconstruction: don't capture UseBB in lambdas, take it as argument

In a following patch, UseBB will be detected later,
so capturing it is potentially error-prone (capture by ref vs by val).

Also, parametrized UseBB will likely be needed
for multiple levels of PHI indirections later on anyways.