Fix arginfos of required arguments for some Reflection methods

[carusogabriel]

Reopening #3443 against master branch (PHP 8.0 now).

This fixes: #74035 and #71416.

/cc @Ocramius @Majkl578

[Majkl578]

This is still 👎 from me as it creates a BC break that is not fixable while supporting both PHP 7 and 8 (unless using conditional code).

[nikic]

@Majkl578 You can, using function invoke($object, $arg1 = null), which is compatible with both function invoke($object, $arg1) and function invoke($object). In fact, you probably already do this (unless your invoke override is completely unused), because otherwise you'd obviously run into argument count errors. Proof: https://3v4l.org/6oIIF

[Majkl578]

@nikic Fair. 👍
But please document this in upgrading guide as a BC break.

[nikic]

@carusogabriel Please combine this PR and #3798. Let's directly go to the correct variadic signature instead of doing this in two steps...

[carusogabriel]

@nikic Okay. Gonna fix a test that's breaking there as well

[nikic]

When merging this, please add an UPGRADING note that mentions all of the old signatures, the new signatures, and the signatures that can be used to be compatible with both.

[carusogabriel]

Merged via 35db1cc. Thanks everyone for the discussion.