[MapServer-dev] Whole code base reformatting

[Even Rouault]

Hi,

Below text from https://github.com/MapServer/MapServer/pull/6937:

I propose to apply to Mapserver the same set of tools that have been 
applied to GDAL and PROJ recently to have consistent code formatting for 
C/C++ and .py files

This uses the pre-commit tool that installs hooks run by git commit to 
automatically apply the formatting rules:

- clang-format for C/C++ code using a .clang-format style based on the 
LLVMStyle with a minimal customization to do 2-space indentation (which 
is the general practice in Mapserver), and not sorting includes (as this 
breaks compilation due to includes unfortunately not being 
clean/standalone, with inconsistencies like "a.h needs a type of b.h, 
but b.h includes a.h"). Third-party code is excluded from reformating 
(in .pre-commit-config.yaml)

- black and isort to format Python code

- flake8 to enforce some rules on Python code (with tons of exceptions 
in .flake8, directly borrowed from the ones of GDAL). I had to manually 
fixup a few things in the .py files

Cf https://gdal.org/development/rfc/rfc69_cplusplus_formatting.html on 
how to install pre-commit (one time operation to do), and 
https://gdal.org/development/dev_practices.html#commit-hooks

A .git-blame-ignore-revs file is also added to identify the reformatting 
commit as to be ignored for the purpose of "git blame". It needs to be 
manually declared to git with "git config blame.ignoreRevsFile 
.git-blame-ignore-revs", for local use (one time operation) but it is 
automatically pickedup by GitHub.

We should probably apply that to the stable branch as well to make 
backports easier.

This also adds a .github/workflows/code_checks.yml GitHub Action that 
runs pre-commit on pull requests to detect violations. Such sitaution 
shouldn't happen for developers that have already set it up locally, but 
useful to catch issues coming from casual contributors (e.g. simulation 
of a commit that would break formatting: 
https://github.com/rouault/mapserver/actions/runs/6340096023/job/17220740975)

Upon acceptance, I'll add a "Code formatting rules" section to 
https://mapserver.org/development/index.html to gather all above information

Even

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