RFR: JDK-8301983: Refactor MEMFLAGS and AllocFailStrategy

[Justin King]

- Rename `MEMFLAGS` to `MemoryType`. `MEMFLAGS` is highly misleading as flags typically can be combined.
- Update `MemoryType` to have enumeration names that follow the style guide, no `mt` prefix.
- Create aliases for old `mtXXX` names.
- Remove `mt_number_of_types` from the enumeration.
- Shift implementation of utilities related to `MEMFLAGS` from `NMTUtil` to `MemoryTypes`. Handle missing `mt` prefix during parsing.
- `NMTUtil` references are not updated to avoid increasing patch size.
- Merge `AllocFailStrategy` and `AllocFailType` into `AllocationFailureStrategy`.
- Move `MemoryType` and `AllocationFailureStrategy` to their own respective headers.

This change does not update variable verbiage. That should be something done over time.

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

Commit messages:
 - Fix undefined variable reference
 - Cleanup memory types and allocation failure strategies

Changes: https://git.openjdk.org/jdk/pull/12454/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12454&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301983
  Stats: 794 lines in 80 files changed: 213 ins; 94 del; 487 mod
  Patch: https://git.openjdk.org/jdk/pull/12454.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12454/head:pull/12454

PR: https://git.openjdk.org/jdk/pull/12454