Resolve properties within annotation bodies

[mimischi]

Go to definition and hover on a property inside an annotation body, like
language in @SourceCode { language = "Pkl" }, resolved to the
annotation class instead of the property. The PklDeclaredTypeImpl of
an annotation spans the whole annotation including its body, so
findBySpan() never made it down to the property.

While adding tests for it, I noticed test has only been running the
snippet tests since #33, so
GoToDefinitionTest, HoverTest and friends never ran in CI. Fixed that
too, otherwise the new tests would not run either.

[bioball]

LGTM, thank you!