RFR: JDK-8301983: Refactor MEMFLAGS and AllocFailStrategy [v5]

[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.

Justin King has updated the pull request incrementally with one additional commit since the last revision:

  Add precompiled header
  
  Signed-off-by: Justin King <jcking at google.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12454/files
  - new: https://git.openjdk.org/jdk/pull/12454/files/61596ca6..eaa44d06

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12454&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12454&range=03-04

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 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