[FuncSpec] Increase the maximum number of times the specializer can run.

* Changes the default value of FuncSpecMaxIters from 1 to 10.
  This allows specialization of recursive functions.
* Adds an option to control the maximum codesize growth per function.
* Measured ~45% performance uplift for SPEC2017:548.exchange2_r on
  AWS Graviton3.

Differential Revision: https://reviews.llvm.org/D145819