[PLAT-6281] Remove reliance on AppKit to allow use in daemons

[nickdowell]

Goal

Allows Bugsnag to be used in macOS executables without linking AppKit.

This matters because some frameworks, such as AppKit, are not safe to use in daemons or executables that run in a non-UI session (bootstrap namespace) as documented in  Technical Note TN2083: Daemons and Agents.

Design

See #919

Changeset

• CLANG_MODULES_AUTOLINK has been set to NO for Bugsnag-macOS in the top-level Bugsnag project - this will cause a build failure if we reintroduce a link-time dependency on AppKit e.g. Undefined symbol: _OBJC_CLASS_$_NSApplication
• Messages to AppKit classes now use NSClassFromString() (via macros) to avoid linking against the class symbol
• Notification names are now hardcoded
• NSProcessInfo.processInfo.processName is now used if NSBundle.mainBundle.bundleIdentifier is nil to prevent ~/Library/Application Support/com.bugsnag.Bugsnag/(null) being used as the storage location for executables that have no Info.plist.

Testing

• Added a unit test case to verify that the hard-coded notification names match those used by the OS.
• Manually verified that Bugsnag works when used in an executable that has no CFBundleIdentifier

[github-actions]

Infer: No issues found 🎉

OCLint: No issues found 🎉

Bugsnag.framework binary size did not change - 1,119,520 bytes

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