Fix interaction between template type and union type

[arnaud-lb]

Fixes phpstan/phpstan#5591

Normally, a UnionType A accepts an other UnionType B if every member of B is accepted by A.

This does not hold if B is a TemplateUnionType: If B is a TemplateUnionType and A contains B, then no member of B will be accepted by B itself, and A will not accept B as a result.

For UnionType::accepts(TemplateUnionType) to work, we must treat it as a non-UnionType.

[ondrejmirtes]

I love this! This is gonna pull out a huge thorn out of my heel! (Yeah, that's a Czech saying)

Feel free to mark it as ready for merge :)

[arnaud-lb]

We have a very similar saying in France: "pull a thorn out of my foot " 😄

I've marked the PR as ready for merge 👍

[ondrejmirtes]

Thank you! Can't wait what other issues this fixes, the bot will find out 😊

[arnaud-lb]

This created a regression: int|float is not a super type of T of int|float anymore. I'm looking into this.

[VincentLanglet]

Hi @arnaud-lb, maybe you can help me on an issue between Tempalte type and Intersection type.
phpstan/phpstan#5336

I've made #585 but ondrej didn't feel the solution as right, WDYT ? Do you see a better way ?