Improve GDExtension tutorial based on own experience

[Maarrk]

• Changed code sample to runtime class to match GDScript default.
  • Recorded a new animation showing the desired result inside game window.
• Changed the wording around SConstruct file to make it less intimidating.
• Added link to IDE setup in building from source documentation.

(original summary)

• Clarified that there is a difference from _process in GDScript that took me by surprise
• Changed the wording around SConstruct file to make it less intimidating.
• Added some hints for usage with third party libraries:
  • I know the tutorial is promised, but maybe this will help someone start writing it ;-)
  • This is my main use case for GDExtension
  • There seems to be some interest in the community: How to bind to external libraries with GDExtension #10301
• Things that can be done with SCons to improve editor functionality, especially relevant due to lack of C++ documentation

[paddy-exe]

First off: Thank you very much for your contribution!
The first two reworded/added section could be IMHO added with some more work. The last section should not be added due to it oversimplifying the process of integrating external libraries.

I personally have been already researching this topic for a while now and do have plans to write the documentation page for this. This would include how to set up external libraries with package managers like vcpkg and conan but also integrating one via git submodules. I have simple projects for these three cases working already but haven't had the time to write the page yet.

[paddy-exe]

One more little nitpick and then I think it's ready to go

[tetrapod00]

Looks good. Ideally the GIF would be an webm video instead, if we're already taking the time to update it (see here for guidelines), but I don't consider that blocking.

[Maarrk]

Well, @tetrapod00 I'd say it's blocking now...

I don't know what to do with it, adding :width: 100% changed nothing

[Maarrk]

Marking as draft so it's not merged until we resolve the video width issue.

I think it's worth doing it because the gif was 2MB for 5 seconds, and webm is 300KB for 10 seconds. I think the static parts of the window compressed really well

[Maarrk]

Thanks for the alignment solution!

It's funny how the PR has almost completely different scope than what I started with, but I'm happy to help you get what's best according to people with experience.

I currently don't have access to the PC, so I can do the squash tomorrow evening. But if you have a convenient way to do it, feel free to merge :-)

[tetrapod00]

Built locally (using a variation on the command snippet from your other PR 😛) and the video renders fine (but left-aligned until the larger fix is merged).

[Maarrk]

Fresh from the oven, rebased, squashed and ready to merge! o7