RFR: 8334137: Marlin: replace sun.misc.Unsafe memory access methods with FFM [v8]

[Kevin Rushforth]

> PR to replace the use of sun.misc.Unsafe memory access methods in the Marlin rasterizer with FFM.
> 
> I broke this up into the following commits. The bulk of the work is in the first two:
> 
> 1. Encapsulate all off-heap access in OffHeapArray -- All of the memory allocation and management was already done in the OffHeapArray class, but the users of OffHeapArray, primarily Renderer and RendererNoAA, called Unsafe methods directly. I encapsulated all of the calls to Unsafe in OffHeapArray. The main impact on calling code is that the base address is no longer accessible or needed. Instead, the `(put|get)(Byte|Int)` methods take only an offset. This commit was straight refactoring with no behavioral changes.
> 2. Initial FFM implementation -- I changed the memory management and access methods to use FFM. Each OffHeap array uses a shared Arena to manage the single memory segment allocated at construction time. The resize method creates a new Arena and memory segment, copying the data from the old and then closing it
> 3. Set `used` to 0 in `dispose()` -- While testing and instrumenting the code, I discovered that the Renderer dispose methods resize the edges array back to the default size without clearing the "used" field. The used field will be cleared before the next time it is accessed, but clearing it in dispose allows optimizing resize to not copy any data.
> 4. Remove '--sun-misc-unsafe-memory-access=allow' from test and app execution, since it is no longer needed. This also enables `-Werror` for the `javafx.graphics` module.
> 5. ~~Temporary debug prints that will be removed before making this "rfr"~~
> 
> Additional commits address review comments.

Kevin Rushforth has updated the pull request incrementally with two additional commits since the last revision:

 - Use the global arena for the ALPHA_MASK arrays.
 - Revert "Initialize alpha maps in constructor to ensure they are created on the right thread (QuantumRenderer)"
   
   This reverts commit 2dd7a35d2eec16b04de1f4cb7aeba31be5d98a55.

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1814/files
  - new: https://git.openjdk.org/jfx/pull/1814/files/2dd7a35d..6c38c604

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1814&range=07
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1814&range=06-07

  Stats: 57 lines in 2 files changed: 43 ins; 4 del; 10 mod
  Patch: https://git.openjdk.org/jfx/pull/1814.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1814/head:pull/1814

PR: https://git.openjdk.org/jfx/pull/1814