Improve build speed [manually] (forward-declarations/clean up includes/etc.)

[Geometror]

This PR aims to improve compilation time by forward-declaring some classes whenever possible/when it makes sense and cleaning up/moving some include statements. There is still some more room to improve, but I think this should be done in subsequent PRs as this manual process of finding optimization opportunities can be very time consuming.

Changes:

• Add forward-declarations of EditorFileDialog and EditorNode to several classes. This is already done in some cases, but not consistently.
• Remove unused includes of file_dialog.h
• Remove forward-declaration of Container in flow_container.h as it was used as a base class which can cause problems. (could be moved to a separate PR)
• Optimize includes in EditorNode and sort forward declarations
• Make missing relative includes (primarily editor includes) absolute for consistency

Some benchmarks (as of Feb 11 2022):
[Time of rebuild. before -> this PR]

Change in progress_dialog.h
28s -> 23s (~17% reduction)

Change in dependency_editor.h
25s -> 23s (~8% reduction)

Change in editor_data.h
3:55m -> 3:01m (~23% reduction)

Change in file_dialog.h
3:47m -> 21s (~91% reduction)

Change in line_edit.h
4:37m -> 3:50m (~17% reduction)

Changed all files above:
4:30m -> 3:56 (~13% reduction)

[Calinou]

This is a good start, nice work 🙂

Did you see #57569 by the way?

[Geometror]

@Calinou Thats quite interesting, will see what I can do with that :)
I am currently trying to create a dependency graph of the godot codebase to find some more optimization opportunities. Does anyone know a good tool (Windows/Linux) to render large/complex graphs and analyze them? I already have the DOT data.

[Calinou]

There's include-what-you-use but I don't know how difficult it would be to run on a SCons-using codebase.

[akien-mga]

There's include-what-you-use but I don't know how difficult it would be to run on a SCons-using codebase.

It's not too difficult, it just needs a wrapper script. I ran it a few years ago, but it's not trivial to make good use of it as it affects the whole codebase.

When using it, a good first step would be to try to sort includes in core only (and anything else that requires changes due to core include changes).

[Geometror]

@Calinou @akien-mga
As you said, getting it to work was straight-forward, however there are problems which makes it quite difficult to make good use of it:

• Sometimes it removes includes of generated headers
• platform specific includes are added (this can be easily fixed though)
• it fails at some complex templates (with specializations) which are declared across multiple files

Tried it in core but couldn't get it to work because of the last point above. It always fails at the GetTypeInfo template and I don't know why. If someone wants to have a look at it:
https://github.com/Geometror/godot/tree/iwyu-core-1

EDIT: Works now. See #57760.

[akien-mga]

Excellent work overall! I reviewed the whole diff and commented on some style issues and a couple problems, but that's a big improvement already as is.

[Geometror]

Fixed all issues, except the ones regarding the dependency editor header as suggested. I was tempted to fix those, but there are still many places left where a similar cleanup could be done so this is indeed material for another PR :)

[akien-mga]

Thanks a lot! I know this was tedious work but it's really appreciated :)