Move initialize_physics to own file

[brownl83]

Tested versions

Reproducible in 4.3 stable - 0dda6a9

System information

Windows 11 - Godot 4.3

Issue description

Enhancement request: Move initialize_physics() function from main.cpp to a dedicated file

Current location: main.cpp line 317
Current implementation:
// FIXME: Could maybe be moved to have less code in main.cpp.
void initialize_physics() {
#ifndef 3DDISABLED
/// 3D Physics Server

Moving this function to its own file would:

Reduce main.cpp complexity
Improve code organization
Address existing FIXME comment

No existing issue was found addressing this FIXME comment.

Steps to reproduce

Steps to verify:

1. Open main.cpp
2. Locate initialize_physics() function at line 317
3. Note FIXME comment indicating the need to move the function
4. Search through open issues for "initialize_physics" or "main.cpp cleanup"
5. Verify no existing issue addresses this FIXME

Expected outcome: Issue tracking for moving initialize_physics() function to dedicated file, as suggested by existing FIXME comment.

Minimal reproduction project (MRP)

main.zip

[AThousandShips]

This kind of tracking is best done in a dedicated tracker such as:

• [TRACKER] Typos and UI Paper Cuts #91521

We don't need dedicated issues tracking code TODOs I'd say