RFR: JDK-8266670: Better modeling of access flags in core reflection [v13]

[Joe Darcy]

> This is an early review of changes to better model JVM access flags, that is "modifiers" like public, protected, etc. but explicitly at a VM level.
> 
> Language level modifiers and JVM level access flags are closely related, but distinct. There are concepts that overlap in the two domains (public, private, etc.), others that only have a language-level modifier (sealed), and still others that only have an access flag (synthetic).
> 
> The existing java.lang.reflect.Modifier class is inadequate to model these subtleties. For example, the bit positions used by access flags on different kinds of elements overlap (such as "volatile" for fields and "bridge" for methods. Just having a raw integer does not provide sufficient context to decode the corresponding language-level string. Methods like Modifier.methodModifiers() were introduced to cope with this situation.
> 
> With additional modifiers and flags on the horizon with projects like Valhalla, addressing the existent modeling deficiency now ahead of time is reasonable before further strain is introduced.
> 
> This PR in its current form is meant to give the overall shape of the API. It is missing implementations to map from, say, method modifiers to access flags, taking into account overlaps in bit positions.
> 
> The CSR https://bugs.openjdk.java.net/browse/JDK-8281660 will be filled in once the API is further along.

Joe Darcy has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 20 additional commits since the last revision:

 - Fix some bugs found by inspection, docs cleanup.
 - Merge branch 'master' into JDK-8266670
 - Initial support for accessFlags methods
 - Add mask to access flag functionality.
 - Add test for location disjointness
 - Minor cleanup.
 - Merge branch 'master' into JDK-8266670
 - Switch to location enum.
 - Respond to review feedback.
 - Add support for module flags; fix typo.
 - ... and 10 more: https://git.openjdk.java.net/jdk/compare/22fa6cf0...a43f7337

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7445/files
  - new: https://git.openjdk.java.net/jdk/pull/7445/files/e8f5b7d7..a43f7337

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7445&range=12
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7445&range=11-12

  Stats: 1819 lines in 40 files changed: 1595 ins; 106 del; 118 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7445.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7445/head:pull/7445

PR: https://git.openjdk.java.net/jdk/pull/7445