RFR: 8278021: Fix warnings in macOS glass native code and treat warnings as errors

[Martin Fox]

Turning on warnings-as-errors for the macOS glass native code. Deprecated declarations are excluded and still appear as warnings.

In the code that tries to locate the application's dock icon there were three instances where `NO` was being passed into a method that required a pointer to a `BOOL`, not a `BOOL`. I suspect the intent was to check that the path pointed to an existing file but not a directory. Since JavaFX has gone this long without screening out directories correctly I decided not to fix that behavior except at the very end.

The only other changes of note are sending some NSNotification objects to delegate API's that require them even though we know they're ignored on the other side. It was the easiest way to get rid of the warning.

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Commit messages:
 - Mac Glass treats errors as warnings except for deprecated declarations

Changes: https://git.openjdk.java.net/jfx/pull/687/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=687&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278021
  Stats: 20 lines in 8 files changed: 12 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jfx/pull/687.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/687/head:pull/687

PR: https://git.openjdk.java.net/jfx/pull/687