Meta-annotations are unnecessarily synthesized in MergedAnotations

[sbrannen]

While analyzing the claim in #28702, I discovered that meta-annotations are unnecessarily synthesized when attempting to synthesize a MergedAnnotation retrieved via the MergedAnnotations.from(AnnotatedElement, ...).get(<annotationType>) API.

This is a regression in our merged annotation support introduced when the MergedAnnotations API replaced our previous support, and the source of the bug is the logic in TypeMappedAnnotation#createSynthesized().

In theory, I could have detected this regression earlier when I had to change a test in BootstrapUtilsTests (see commit ce87285), since @BootstrapWith should never have been synthesized; however, I overlooked that detail at the time.