RFR: 8327152: NMT: use BitMap for committed memory regions in summary mode

[Afshin Zafari]

In summary mode, we don't show/use the stack traces. So, it is possible to use `BitMap` for sub-regions of a reserved region. A bit is used for every page in the reserved region and is 1 when committed and 0 when uncommitted.
No need to handle split/merge/exclude and any other similar operations on sub-regions. We just set/clear the bits accordingly.

To find the actual amount of committed/uncommitted memory, we just count the 1 bits before the operation and adjust the request size appropriately. For example:

                                              1         2
Bit index:                          01234567890123456789012
Current state of a reserved region: 11111000000111110000111
commit sub-region [8,15):                   ^-----^       
already-committed = 4
actual-committed = (15 - 8) - 4 = 3

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Commit messages:
 - 8327152: NMT: use BitMap for committed memory regions in summary mode

Changes: https://git.openjdk.org/jdk/pull/18090/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18090&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327152
  Stats: 79 lines in 3 files changed: 71 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/18090.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18090/head:pull/18090

PR: https://git.openjdk.org/jdk/pull/18090