RFR: 8337563: NMT: rename MEMFLAGS to MemTag

[Gerard Ziemski]

Please review this cleanup, where we rename `MEMFLAGS` to `MemTag`.

`MEMFLAGS` implies that we can use more than one at the same time, but those are exclusive values, so `MemTag` is a more suitable name.

This fix also includes a cleanup of all the related parameter names and local variable names.

Testing is pending...

Note: there is more history in old closed PRs [https://github.com/openjdk/jdk/pull/20497](https://github.com/openjdk/jdk/pull/20497) and [https://github.com/openjdk/jdk/pull/20472](https://github.com/openjdk/jdk/pull/20472)

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Commit messages:
 - missed renames on Windows
 - fix test failure
 - fix incorrect rename
 - mssing renames
 - missed _mem_type --> _mem_tags
 - missed MemFlagBitmap --> MemTagBitmap
 - missed tag --> mem_tag
 - missed type --> tag
 - missed type --> tag
 - missed flag_is_valid --> tag_is_valid
 - ... and 1 more: https://git.openjdk.org/jdk/compare/4ffcf894...983bb6e2

Changes: https://git.openjdk.org/jdk/pull/20872/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20872&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337563
  Stats: 1259 lines in 108 files changed: 142 ins; 138 del; 979 mod
  Patch: https://git.openjdk.org/jdk/pull/20872.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20872/head:pull/20872

PR: https://git.openjdk.org/jdk/pull/20872