Inlining heuristics for `FunctionSpecializer`

## Abstract and Motivation

This mainly came up in https://twitter.com/d1ll0nk/status/1600472867661295616. In short, for code where function pointers are used as arguments, `FunctionSpecializer` would end up specializing the function (because the function pointers would be constants). This may lead to code that's not ideal.

## Specification

Use a similar heuristic to the `FullInliner` in the `FunctionSpecializer`. The original context for `FunctionSpecializer` was to handle cases that the `FullInliner` couldn't do. So we have to rethink and benchmark this again, especially since the inline heuristics were changed after the new Yul code transform.

Locate the FunctionSpecializer and FullInliner implementations and compare their current inlining heuristics. Review how the heuristics changed with the new Yul code transform, then benchmark function-pointer cases and confirm that specialization no longer produces undesirable code.

Written by the indexing model from the issue text.