RFR: 8371106: [macOS] Min/max window height is incorrect for EXTENDED StageStyle

[Michael Strauß]

This patch fixes window size contraints for an `EXTENDED` stage. In contrast to the suggested workaround in the JBS ticket of querying the value of [`NSWindow.minSize`](https://developer.apple.com/documentation/appkit/nswindow/minsize?language=objc) to find out the added size for the toolbar, I've found it easier to set the [`NSWindow.contentMinSize`](https://developer.apple.com/documentation/appkit/nswindow/contentminsize?language=objc) property instead.

This is only done for `EXTENDED` stages, preserving the existing behavior for all other stage styles, and it works because extended stages use a full-size content view that covers the entire window. It also makes it unnecessary to take the toolbar height into consideration, which would be necessary if we used the `minSize` property instead.

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Commit messages:
 - fix

Changes: https://git.openjdk.org/jfx/pull/1967/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1967&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371106
  Stats: 18 lines in 2 files changed: 15 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jfx/pull/1967.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1967/head:pull/1967

PR: https://git.openjdk.org/jfx/pull/1967