doc: Update classref with node renames

SCons: Treat all warnings as errors

Move glow upscale quality to a global setting, for consistency

After an effort spanning several years, we should now be warning-free
on all major compilers, so we can set `-Werror` to ensure that we don't
introduce warnings in new code.

Disable -Werror=strict-overflow on GCC 7 though, as it seems bogus and
was fixed in 8+.

And simplify code in CSGShape.

A few extra renames for classes which were missed in last week's PRs.

SCons: Format buildsystem files with psf/black

Also install and use pygmentize to visualize clang-format and black
diffs.

Configured for a max line length of 120 characters.

psf/black is very opinionated and purposely doesn't leave much room for
configuration. The output is mostly OK so that should be fine for us,
but some things worth noting:

- Manually wrapped strings will be reflowed, so by using a line length
  of 120 for the sake of preserving readability for our long command
  calls, it also means that some manually wrapped strings are back on
  the same line and should be manually merged again.

- Code generators using string concatenation extensively look awful,
  since black puts each operand on a single line. We need to refactor
  these generators to use more pythonic string formatting, for which
  many options are available (`%`, `format` or f-strings).

- CI checks and a pre-commit hook will be added to ensure that future
  buildsystem changes are well-formatted.

Properly handle node remove via undo

Prevent shader crash if multiple variables has been declared in 'for'

Alias `platform=x11` to `platform=linuxbsd` in SCons

This makes it possible for users to follow outdated documentation
and still get a working binary.

This closes #37367.

Fix for loop range bug: #37358

Ensure COWData does not always reallocate on resize, fixes #22561

Remove the audio memory allocator, use regular one instead.

More server renames for consistency after #37361

Fixed probable typo in renaming.

Renaming of servers for coherency.

VisualServer -> RenderingServer
PhysicsServer -> PhysicsServer3D
Physics2DServer -> PhysicsServer2D
NavigationServer -> NavigationServer3D
Navigation2DServer -> NavigationServer2D

Also renamed corresponding files.

Make 2D and 3D node names more explicit

Rename editor plugins to match the new node names.

DisplayServer: Fix registration of GetRenderingDriversFunction

Fix default editor font.

Fixes #30736.

Fix some -Wmaybe-uninitialized warnings

Namely:
```
modules/basis_universal/register_types.cpp: In function 'Ref<Image> basis_universal_unpacker(const Vector<unsigned char>&)':
modules/basis_universal/register_types.cpp:266:15: warning: 'imgfmt' may be used uninitialized in this function [-Wmaybe-uninitialized]
  266 |  image->create(info.m_width, info.m_height, info.m_total_levels > 1, imgfmt, gpudata);
      |  ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
modules/basis_universal/register_types.cpp:255:39: warning: 'format' may be used uninitialized in this function [-Wmaybe-uninitialized]
  255 |    bool ret = tr.transcode_image_level(ptr, size, 0, i, dst + ofs, level.m_total_blocks - i, format);
      |               ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

```
servers/visual_server.cpp: In member function 'Error VisualServer::_surface_set_data(Array, uint32_t, uint32_t*, uint32_t, Vector<unsigned char>&, int, Vector<unsigned char>&, int, AABB&, Vector<AABB>&)':
servers/visual_server.cpp:636:15: warning: 'iw' may be used uninitialized in this function [-Wmaybe-uninitialized]
  636 |       copymem(&iw[i * 2], &v, 2);
      |               ^
```

```
core/image.cpp: In member function 'Error Image::generate_mipmap_roughness(Image::RoughnessChannel, const Ref<Image>&)':
core/image.cpp:1683:11: warning: 'roughness' may be used uninitialized in this function [-Wmaybe-uninitialized]
 1683 |     float roughness;
      |           ^~~~~~~~~
```