Style: Harmonize header guards to style guide [Core]

[akien-mga]

Reviewed all core/ headers to ensure that they have header guards that match their file name, and and that the last #endif includes the name of the guard as comment, as in our guidelines: http://docs.godotengine.org/en/latest/community/contributing/code_style_guidelines.html#header-includes

I'll leave the rest of the codebase for another contributor to have a look at, but instead of doing it manually, I would suggest writing a script that we can use periodically to parse and fix the codebase, as we do with misc/scripts/fix_headers.py. Some special cases need to be handled too as those added in #37143 (i.e. guards which don't directly match their file name to avoid duplicates).

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To review header guards for all headers:

find -name thirdparty -prune -o -name "*.h" | sort > headers
for file in $(cat headers); do echo -e "\n$file"; grep "#ifndef .*_H" $file; done > output