[lworld] RFR: 8287330: (valhalla) Better modeling of access flags in core reflection

[Roger Riggs]

Import, verbatim, the new API for access flags to Valhalla;  (Not in mainline until jdk 20).
The API is unmodified from the mainline version. [Mainline Review openjdk/jdk/7445](https://git.openjdk.java.net/jdk/pull/7445) 

The Valhalla modifiers will be added in the new AccessFlags class in a subsequent PR.
The existing Modifiers class will not include Valhalla specific modifiers.

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Commit messages:
 - 8287330: (valhalla) Better modeling of access flags in core reflection

Changes: https://git.openjdk.java.net/valhalla/pull/697/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=697&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287330
  Stats: 761 lines in 9 files changed: 745 ins; 2 del; 14 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/697.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/697/head:pull/697

PR: https://git.openjdk.java.net/valhalla/pull/697