[InlineCost]: Add a new heuristic to branch folding for better inlining decisions.

Recursive functions are generally not inlined to avoid issues 
like infinite inlining or excessive code expansion. However,
this conservative approach misses opportunities for optimization in
cases where a recursive call is guaranteed to execute only once.

This patch detects a scenario where a guarding branch condition of a recursive
call will become false after the first iteration of the recursive function.
If such a condition is met, and the recursion depth is confirmed to be one,
the Inliner will now consider this recursive function for inlining.

A new test case (`test/Transforms/Inline/inline-recursive-fn.ll`)
has been added to verify this behaviour.

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