Variadic params should always be optional and fix redundant optional variadic annotation

[kkmuffme]

• fix variadic params have wrong type in PHP 8/8.1
• Fix PHP variadic internal functions should not allow named calls #10787
• add error when using named arguments in PHP <8
• fix report an error in all cases when unpacking string keyed array in PHP < 8.1 in all cases (reported for < 8.0 in some incorrectly)
• fix no errors reported for unpacked union (e.g. array|int)
• fix keyed array with fallback didn't report the same errors as unkeyed array for toomany/toofewarguments
• add error for possibly too many/few arguments with array unpacking
• fix named arguments after positional arguments not reported in unpacking
• fix Inconsistent handling of "empty"-status of arrays as return values #9188

[kkmuffme]

@weirdan review and merge please

[weirdan]

189 new errors reported in PHPUnit look quite worrying: https://app.circleci.com/pipelines/github/vimeo/psalm/13214/workflows/7c12912e-4b6a-4e48-9ba6-06a9d0015c09/jobs/43049

[kkmuffme]

Went through them quickly and they're all correct in terms of that we cannot be certain that there's not a bug hidden.
Is it annoying when using spread operator? Definitely yes. However practically, the spread operator was an escape hatch for strict type checking and the fix is often quite simple (set actual array keys as int if you only accept int arrays, use non-empty-array type) but the impact rather big (since those would be fatal errors in many cases)