RFR: 8334495: Use FFM instead of jdk.internal.misc.Unsafe in java.desktop font implementation

[Phil Race]

Migrate font code from jdk.internal.misc.Unsafe to using FFM.
This reduces the coupling between the java.desktop module and the internals of the java.base module.

The code being changed here is not particularly performance sensitive, and it is not executed in the most common cases.
The main impact performance-wise is a total of around 37ms in initialisation costs on my x64 macbook.
A minimal program that just draws a string to an image - does not even put up a window - runs at around 690-700ms.
There's variability in that number and the overall time for a JDK without the change is around (660-670ms)
In the small test, this is the first and only use of FFM, so the one-off part cost should move elsewhere when FFM starts
to be used earlier in the JDK itself.

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

Commit messages:
 - 8334495
 - 8334495

Changes: https://git.openjdk.org/jdk/pull/19777/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19777&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334495
  Stats: 317 lines in 5 files changed: 133 ins; 91 del; 93 mod
  Patch: https://git.openjdk.org/jdk/pull/19777.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19777/head:pull/19777

PR: https://git.openjdk.org/jdk/pull/19777