RFR: 8303431: [JVMCI] libgraal annotation API [v6]

[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.

Doug Simon has updated the pull request incrementally with one additional commit since the last revision:

  addressed review feedback

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12810/files
  - new: https://git.openjdk.org/jdk/pull/12810/files/a85fa13a..abaf2375

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12810&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12810&range=04-05

  Stats: 10 lines in 2 files changed: 0 ins; 9 del; 1 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