Add common flags and options

[rsore]

Description

A lot of programs support the same basic flags and options, for exampe "--help", "--verbose" and "--input ". It makes sense for the library to offer a set of these basic flags and options ready for use so users don't necessarily have to create custom flags and options for everything. They can simply be added to the parser builder and used directly:

auto parser = CLArgs::ParserBuilder{}
    .add_flag<CLArgs::CommonFlags::Verbose>()
    .add_option<CLArgs::CommonOptions::Input>()
    .add_option<UserDefinedCustomOption>()
    .build();

...

if (parser.has_flag<CLArgs::CommonFlags::Verbose>())
{
    // Enable verbose output
}

Related Issues

Closes #32.

How Has This Been Tested?

I implemented tests for all common flags and options I added. The tests themselves do not check behavior in cases like ill-formed values or unknown arguments, these are already handled in other tests. Instead, these simply focus on verifying that the flag and option types can be used with the parser, and that the values are properly set for any of their supported identifiers.

[github-actions]

clang-tidy made some suggestions

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"