RFR: 8303431: [JVMCI] libgraal annotation API

[Doug Simon]

This PR extends JVMCI with new API (`jdk.vm.ci.meta.Annotated`) for accessing annotations. The main differences from `java.lang.reflect.AnnotatedElement` are:
* Each `Annotated` method explicitly specifies the annotation type(s) for which it wants annotation data. That is, there is no direct equivalent of `AnnotatedElement.getAnnotations()`.
* Annotation data is returned in a map-like object (of type `jdk.vm.ci.meta.AnnotationData`) instead of in an `Annotation` object. This works better for libgraal as it avoids the need for annotation types to be loaded and included in libgraal.
 
To demonstrate the new API, here's an example in terms `java.lang.reflect.AnnotatedElement` (which `ResolvedJavaType` implements):

    ResolvedJavaMethod method = ...;
    ExplodeLoop a = method.getAnnotation(ExplodeLoop.class);
    return switch (a.kind()) {
        case FULL_UNROLL -> LoopExplosionKind.FULL_UNROLL;
        case FULL_UNROLL_UNTIL_RETURN -> LoopExplosionKind.FULL_UNROLL_UNTIL_RETURN;
        ...
    }


The same code using the new API:


    ResolvedJavaMethod method = ...;
    ResolvedJavaType explodeLoopType = ...;
    AnnotationData a = method.getAnnotationDataFor(explodeLoopType);
    return switch (a.getEnum("kind").getName()) {
        case "FULL_UNROLL" -> LoopExplosionKind.FULL_UNROLL;
        case "FULL_UNROLL_UNTIL_RETURN" -> LoopExplosionKind.FULL_UNROLL_UNTIL_RETURN;
        ...
    }


The implementation relies on new methods in `jdk.internal.vm.VMSupport` for parsing annotations and serializing/deserializing to/from a byte array. This allows the annotation data to be passed from the HotSpot heap to the libgraal heap.

-------------

Commit messages:
 - made AnnotationDataDecoder package-private
 - add annotation API to JVMCI

Changes: https://git.openjdk.org/jdk/pull/12810/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12810&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303431
  Stats: 2666 lines in 33 files changed: 2614 ins; 24 del; 28 mod
  Patch: https://git.openjdk.org/jdk/pull/12810.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12810/head:pull/12810

PR: https://git.openjdk.org/jdk/pull/12810