Improve macOS HIG compliance of Close and Close All menu items.

[freakboy3742]

The menu items used for Close and Close All follow the example of Safari, which is a bit of an oddity when compared to most other macOS apps.

This PR changes the default macOS menu items to match the more common naming and shortcuts:

• "Close Window" (CMD-SHIFT-W) -> "Close" (CMD-W)
• "Close All Windows" (CMD-OPT-SHIFT-W) -> "Close" (CMD-OPT-W)

Fixes #2214.

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[mhsmith]

My first thought was that Close All is the same as Quit because we don't yet support running an app without any windows. But since people have it in their muscle memory, we should support it anyway.