Fix multiple recent Bullet physics crashing issues.

[madmiraal]

Fixes #40311
Fixes #40840

As elaborated on here and here, #39726 has caused multiple crashing issues (such as #40311 and #40840) which are not being fully resolved with #40252 (see comment) #40886 or #41067 (see comment) Furthermore, it did not solve #30027 for which it was created. Therefore this PR reverts #39726, which also requires reverting #40252.

Note: This PR also includes three additional commits:

1. Improves [Bullet] Area zero gravity with Bullet #40127 (using the change from Call reload_space_override_modificator() directly when processing a body entering or leaving an area. #40186) instead of Improved Bullet Physics flush algorithm, Lazy collision filter reload, Shape reload regression fix. #40252.
2. The fix for [Bullet] Gravity is applied to RigidBody even with custom_integrator turned on #40508 included in Improved Bullet Physics flush algorithm, Lazy collision filter reload, Shape reload regression fix. #40252; but extended to include dampening.
3. A fix for Fixes leak when creating bullet shape #41040 that also relied on a Optimized physics object spawn time #39726.

Finally I've confirmed it does not revert the fix for #40506.

[AndreaCatania]

The benchmark code is this:

extends Node

var count = 0

var shapes_per_frame := 2000
var shape := BoxShape3D.new()
var t1

func _ready():
	t1 = OS.get_ticks_msec()
	_do_test()

func _physics_process(delta):
	if count < 3:
		var t2 = OS.get_ticks_msec()
		count += 1
		print("Frame ", count, ": ", t2 - t1, "ms")
	else:
		get_tree().quit()

func _do_test():
	print("Test start")
	for i in range(0, shapes_per_frame):
		var rb = RigidBody3D.new()
		var c = CollisionShape3D.new()
		c.set_shape(shape)
		rb.add_child(c)
		add_child(rb)
		if i % 50 == 0:
			print("Added: ", i)

This is the benchmark result obtained from this PR on my pc:

Test start
Added: 0
Added: 50
Added: 100
Added: 150
Added: 200
Added: 250
Added: 300
Added: 350
Added: 400
Added: 450
Added: 500
Added: 550
Added: 600
Added: 650
Added: 700
Added: 750
Added: 800
Added: 850
Added: 900
Added: 950
Added: 1000
Added: 1050
Added: 1100
Added: 1150
Added: 1200
Added: 1250
Added: 1300
Added: 1350
Added: 1400
Added: 1450
Added: 1500
Added: 1550
Added: 1600
Added: 1650
Added: 1700
Added: 1750
Added: 1800
Added: 1850
Added: 1900
Added: 1950
Frame 1: 8618ms
Frame 2: 22686ms
Frame 3: 34715ms

This is the result obtained using the current master branch:

Test start
Added: 0
Added: 50
Added: 100
Added: 150
Added: 200
Added: 250
Added: 300
Added: 350
Added: 400
Added: 450
Added: 500
Added: 550
Added: 600
Added: 650
Added: 700
Added: 750
Added: 800
Added: 850
Added: 900
Added: 950
Added: 1000
Added: 1050
Added: 1100
Added: 1150
Added: 1200
Added: 1250
Added: 1300
Added: 1350
Added: 1400
Added: 1450
Added: 1500
Added: 1550
Added: 1600
Added: 1650
Added: 1700
Added: 1750
Added: 1800
Added: 1850
Added: 1900
Added: 1950
Frame 1: 34ms
Frame 2: 8914ms
Frame 3: 13978ms

This is flame graph extracted from the perf of this PR:

This is flame graph extracted from the perf of master branch:

[madmiraal]

Rebased following #42061.

[madmiraal]

Superseded by #42639. I've created #42649 and #42650, and reopened #40186 and #40187 to address the issues addressed by this PR, but not addressed by #42639.