Fix a few issues with the C generator (part 4)

[eafer]

Four more patches from the original pull request at #14379. I reordered the patches this time because the last remaining two are somewhat harder to explain.

@wing328 @ityuhui @zhemant @michelealbano

I ran generate-samples.sh as usual, but I see something off with the results for petstore/c/. Not all of the cmake files are getting updated. I retried multiple times but I can't tell what I'm doing wrong.

EDIT: This PR includes the following changes:

• Add support for binary arguments in the request body
• Add support for enums in the request path
• Update the schemas to test both 1 and 2
• Update the cmake configuration so that headers are installed as well, not just the library
• Update the cmake configuration so that a C++ compiler is not required for the build

[eafer]

So the checks are passing, but I still think something is off because petstore/c is still being built as C++:

-- The C compiler identification is GNU 11.4.0
-- The CXX compiler identification is GNU 11.4.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped

while the other two samples are being built as plain C:

-- The C compiler identification is GNU 11.4.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done

I don't know why this is happening. It does get fixed if I delete the whole sample folder and generate it again, for some reason.

[wing328]

@eafer in the description, can you please list out (point form) what issues are fixed by this PR?

[eafer]

@wing328 I just added the list of changes to the description. Let me know if you need anything else.

[wing328]

Looks good 👍

[eafer]

I just deleted all the C samples and generated them from scratch. I don't understand enough to tell why the result is different, but it looks better now.

[eafer]

I guess that wasn't the right thing to do...

[wing328]

We can improve the CI/tests with another PR instead.

[eafer]

Great, thanks!