Extreme slowdowns when freeing and reallocating many nodes that share the same Mesh

[myaaaaaaaaa]

Godot version

v4.0.beta8.official.45cac42c0

System information

Linux, Vulkan API 1.3.224 - Using Vulkan Device #0: Intel - Intel(R) Iris(R) Plus Graphics 655 (CFL GT3)

Issue description

The following sample code builds a tree of nodes that share the same ArrayMesh. Freeing and then reallocating this tree causes extreme slowdowns.

extends Benchmark

func build_node() -> Node3D:
	var mesh := ArrayMesh.new()
	var rt := MeshInstance3D.new()
	for i in 10_000:
		var n := MeshInstance3D.new()

		####################
		### Removing this line stops the slowdown
		n.mesh = mesh

		rt.add_child(n)
	return rt

####################
### 200 milliseconds
func benchmark_alloc_free_1():
	build_node().free()

####################
### 14 seconds (70x slower)
func benchmark_alloc_free_5():
	for i in 5:
		build_node().free()

Steps to reproduce

Clone the below PR and run the HLOD setup benchmark from the root directory via:
godot-4.0beta8-binary-name -- --run-benchmarks --include-benchmarks=rendering/hlod/setup

Minimal reproduction project

godotengine/godot-benchmarks#23