RFR: 8322215: [win] OS events that close the stage can cause Glass to reference freed memory

[Martin Fox]

When a Stage is closed while processing an OS message the glass peer object is deleted immediately even if it's still executing member functions. As glass unwinds the stack and executes cleanup code it's referencing freed memory.

There are cases where glass generates JavaFX events back-to-back. For example, when handling the Delete key glass sends a PRESSED and TYPED event in the same routine. If the Stage is closed during the PRESSED event the code that sends the TYPED event is running inside an object that has already been deleted.

When the Stage is closed glass calls the OS routine ::DestroyWindow on the HWND causing a WM_NCDESTROY message to be sent. Currently the BaseWnd object is deleted when processing this message. This PR defers the destruction until all messages have been processed. This is the same approach used in the Linux code.

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Commit messages:
 - Window context is only deleted after all messages are processed

Changes: https://git.openjdk.org/jfx/pull/1309/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1309&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322215
  Stats: 32 lines in 2 files changed: 30 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/1309.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1309/head:pull/1309

PR: https://git.openjdk.org/jfx/pull/1309