RFR: 8342993: Remove uses of AccessController and AccessControlContext from JavaFX [v3]

[Kevin Rushforth]

> This PR removes all remaining uses of `AccessController` and `AccessControlContext`, which represent the last remaining uses of the terminally deprecated security APIs except for those in the `/ios/` or `/android/` directories.
> 
> With the removal of doPrivileged and the `if (System.getSecurityManager() != null)` code paths, the ACC is no longer used, so can be completely eliminated. Along with this, I removed all unused imports of security-related APIs and all related `@SuppressWarnings("removal") annotations.
> 
> ### Notes to reviewers
> 
> * Most of the changes were straight-forward removals of methods and fields to save, retrieve and pass around the `AccessControlContext`.
> * The Toolkit class stores a collection of listeners in a `WeakHashMap` with the listener as the key (thus weakly held) and the ACC as the value. We no longer need or want the ACC, but I kept the use of `WeakHashMap` and changed the value type to `Object`, storing a singleton dummy object as the value for each entry. This minimizes the changes, while preserving the behavior of reclaiming the entries when they are garbage collected.

Kevin Rushforth has updated the pull request incrementally with one additional commit since the last revision:

  review feedback

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1638/files
  - new: https://git.openjdk.org/jfx/pull/1638/files/f01faa1e..64556c26

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1638&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1638&range=01-02

  Stats: 24 lines in 2 files changed: 1 ins; 5 del; 18 mod
  Patch: https://git.openjdk.org/jfx/pull/1638.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1638/head:pull/1638

PR: https://git.openjdk.org/jfx/pull/1638