As an experiment to see how performance is impacted when changing
inline definitions to normal definitions in a .cc file, this CL moves
js-function-inl.h to js-function.cc.

Bug: v8:10749
Change-Id: I97c3a0b7d20217f444c6891442bbe3c34f3b0cc9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2315993
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69091}