Remove the dependency on github.com/modern-go/reflect2

[dominiquelefevre]

reflect2 is too brittle because of the reliance on the internals of the golang's compiler. Moreover, it is no longer maintained: github.com/modern-go/reflect2..

Replace the usages of github.com/modern-go/reflect2 with stdlib's reflect.

[fioncat]

Agreed, after i updated go to 1.20, reflect2 panic directly, this is awful.

[pgimalac]

Also for the record reflect2 wraps reflect.Type under the hood, which means when using it the linker considers the Method and MethodByName functions as reachable (even if this library doesn't use them), which disables some dead code elimination, resulting in a significantly bigger binary... (see this talk for more details)

Having this optimization enabled reduced a binary I work on from around 36MB to 29MB.