RFR: 8340103: Add internal set_flag function to VMATree

[Johan Sjölen]

Hi!

The old VirtualMemoryTracker has a method set_reserved_region_type(address, flag). We implement this for the new VMATree implementation by altering the signature slightly to set_reserved_region_type(address, size, flag). This simplifies the implementation greatly for our new data structure and leads to trivial changes for the callers (all callers already know the size).

This PR implements the internal implementation along with tests, but does not change any callers.

I also do a few cleanups:

- Change `Node` to `TreeNode` in tests, we've seen build failures because of this (probably a precompiled headers issue)
- Add a few `print_on` methods for  easy debugging
- Add a `size` alias, it was a bit confusing that some functions took an argument `position sz`, so changed that to `size sz` 

Thanks.

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Commit messages:
 - Only generate if in debug mode
 - Size
 - Forgot to update size and from
 - Oops
 - Fix the tests
 - Introduce size alias
 - Implement set_flag

Changes: https://git.openjdk.org/jdk/pull/20994/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20994&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340103
  Stats: 180 lines in 4 files changed: 170 ins; 1 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/20994.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20994/head:pull/20994

PR: https://git.openjdk.org/jdk/pull/20994