GDScript: Lambda hotswap fixes

[rune-scape]

im glad #85248 got merged and fixed my mistakes from #81628
however,
it has some problems that this PR fixes:

• thread_enter and thread_exit are inadequate for initializing the threadlocal lists, as external thread created by, FMOD for example, arent tracked at all, leading to a segfault when it tries to access the threadlocal list
• Fix lambda cross-thread dynamics (take 2) #85248 is, no offense, over complicated, manual refcounting is unnecessary and error prone, just keeping track of the lists should be used instead of moving orphaned list elements to the main thread list

and,, another thing fixed by this:

• my original code was fundamentally broken
• it nulls lambdas unrelated to the currently reloading script, making hot-reloading lambdas still broken, just safer, no crashing
• just alot safer, regular mutex and data member arrangement,, easy to wrap head around

crucially it works on my project that uses lambdas and needs hot-reloading to properly update them, where the current master commit fails,, lambdas just become invalid for all but 1 script
keeping only the relevant updateable func ptrs in each script with a mutex for each is enough to make this fast and safe in lambda creation, and script reloading and clearing.
and easier to read and modify the code
it should function as i meant it to originally in #81628 and now waste no time checking unrelated elements when reloading

the following recent related bugs are still gone after this PR:

• Deferred call of GDScript lambda from thread leads to double free or corruption when hot reloading #84046
• Lambda call within a non-main thread forces Godot to crash at exit #84190
• Lambda/Callable memory leak #85112

but i could not reproduce #85151, if someone who can reproduce it can test that its still fixed after this PR i would be so grateful
sorry for the wait

[rune-scape]

trying to find out why only the linux builds are failing..

[rune-scape]

#0  0x000000000a2119dd in GDScript::UpdatableFuncPtrOwnerListContainer::UpdatableFuncPtrOwnerListContainer (
    this=0x7fffff400d80) at modules/gdscript/gdscript.cpp:1397
1397    GDScript::UpdatableFuncPtrOwnerListContainer::UpdatableFuncPtrOwnerListContainer() {

oops it seems threadlocal var initializers arent re-entrant safe... only on linux,

i rewrote it to be way simpler anyway,

[RandomShaper]

• Fix lambda cross-thread dynamics (take 2) #85248 is, no offense, over complicated [...].

You should have seen its first iteration. 😆

Now seriously, I did my best to understand the intent of the original code so I could provide a fix. I had to make a few assumptions. I'm happy there's a proper patch now.

[rune-scape]

@RandomShaper you did a good job, it was pretty bad code,,,
i should have gone with simplest option to begin with :)

[RandomShaper]

LGTM. There are change requests by others, I agree with, though.

[akien-mga]

Thanks!

[rune-scape]

i think this should probably be cherry-picked for 4.2 ,, ill make a commit