RFR: 8294982: Implementation of Classfile API [v32]

[Adam Sotona]

> This is root pull request with Classfile API implementation, tests and benchmarks initial drop into JDK.
> 
> Following pull requests consolidating JDK class files parsing, generating, and transforming ([JDK-8294957](https://bugs.openjdk.org/browse/JDK-8294957)) will chain to this one.
> 
> Classfile API development is tracked at:
> https://github.com/openjdk/jdk-sandbox/tree/classfile-api-branch
> 
> Development branch of consolidated JDK class files parsing, generating, and transforming is at:
> https://github.com/openjdk/jdk-sandbox/tree/classfile-api-dev-branch
> 
> Classfile API [JEP](https://bugs.openjdk.org/browse/JDK-8280389) and [online API documentation](https://htmlpreview.github.io/?https://raw.githubusercontent.com/openjdk/jdk-sandbox/classfile-api-javadoc-branch/doc/classfile-api/javadoc/java.base/jdk/internal/classfile/package-summary.html) is also available.
> 
> Please take you time to review this non-trivial JDK addition.
> 
> Thank you,
> Adam

Adam Sotona has updated the pull request incrementally with five additional commits since the last revision:

 - ConstantPoolBuilder::natEntry renamed to nameAndTypeEntry
 - removed static implementation methods from ClassEntry
 - removed unused imports
 - fixed PackageSnipets
 - default constantValue delegating to asSymbol pulled from implementations to  ConstantDynamicEntry, MethodHandleEntry and MethodTypeEntry

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10982/files
  - new: https://git.openjdk.org/jdk/pull/10982/files/1e95e508..70ec5ec7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10982&range=31
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10982&range=30-31

  Stats: 363 lines in 47 files changed: 17 ins; 307 del; 39 mod
  Patch: https://git.openjdk.org/jdk/pull/10982.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10982/head:pull/10982

PR: https://git.openjdk.org/jdk/pull/10982