Support shader preprocessor concatenation symbol

[JohanAR]

[clayjohn]

CC @bitsawer

[Calinou]

Remember to document this change in https://docs.godotengine.org/en/latest/tutorials/shaders/shader_reference/shader_preprocessor.html :slightly_smiling_face:

You can open a draft pull request on godot-docs' master branch now – no need to wait for this PR being merged.

[JohanAR]

Docs PR https://github.com/godotengine/godot-docs/pull/6979

[bitsawer]

Looks good to me after the changes. Tested with my own projects and tests, seems to work as expected. I'll add those tests to my preprocessor test suite and try to eventually make a public PR for it once I have some extra time.

@Chaosus might still want to take a look and give the final approval.

[JohanAR]

Tested and it works fine for me - just add the missing dots to the commentaries.

Thanks! I'm not that used to working with github's web UI, but I think I got all the suggestions. Should I try to squash the branch or will that be done when merging?

[Chaosus]

Should I try to squash the branch or will that be done when merging?

Yes, you should.

[akien-mga]

Thanks!