Improve Collection ::first() and ::last() return type provider.

[AndrolGenhald]

Infer non-empty when Collection::add() has been called, and make provider work for properties as well as variables.

[orklah]

looks like we're gonna have to fix the CI first...

[AndrolGenhald]

Oh wow, yeah...

[AndrolGenhald]

Well this is great, phpstan/phpdoc-parser had a backward incompatible change that broke slevomat/coding-standard (slevomat/coding-standard#1379), and doctrine/coding-standard relies on slevomat/coding-standard ^7.0.0. doctrine/coding-standard 9.0.x updates that to ^8, but there hasn't been a release with that yet, so I'm not sure what to do about it... It's currently impossible to run phpcs without crashing.

[orklah]

Can we pin the version of phpstan/phpdoc-parser to one that doesn't fail?

[AndrolGenhald]

When I run composer update --prefer-dist --no-interaction --prefer-stable --prefer-lowest I get different dependencies and the tests run fine, not sure why it's different yet.

[muglug]

I guess remove the doctrine/coding-standard req until things stabilise?

[AndrolGenhald]

@orklah's suggestion to pin phpstan/phpdoc-parser fixed that one, but I opened a separate pull for that (#120) so it would be clear that it's a requirement that's not needed and can be removed in the future. Not sure what's going on with the low deps tests though.