RFR: API classes supporting RuntimeTypes and ArrayCreation bootstraps

[Dan Smith]

- Introduce the RuntimeType interface
- Modify Class to implement RuntimeType
- Introduce NullRestrictedClass as another implementation of RuntimeType
- Provide ConstantDesc support for NullRestrictedClasses
- Introduce reflection hooks to query RuntimeType of fields and arrays (just return Classes for now)
- Provide ArrayCreation bootstraps to create arrays with RuntimeTypes, initial values, and flags (no runtime support for new features yet—implementation bottoms out at Array.newInstance)
- Basic functionality testing of ArrayCreation bootstraps

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Commit messages:
 - Fix whitespace
 - Introduced RuntimeType interface; provided ArrayCreation bootstraps

Changes: https://git.openjdk.org/valhalla/pull/1210/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1210&range=00
  Stats: 1029 lines in 9 files changed: 1027 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/valhalla/pull/1210.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1210/head:pull/1210

PR: https://git.openjdk.org/valhalla/pull/1210