Add thread checkers to xcscheme.diagnostics

[cerisier]

This PR adds 2 additional diagnostics to xcscheme.diagnostics as configurable in Xcode like below:

---

They are enabled by default for retrocompat but it's also the default in Xcode.

I wasn't sure what naming convention to adopt in this PR because:

1. Those flags in the .xcscheme plist are negative flags, vs the other diagnostics flag which are positive flags:
   1. disableMainThreadChecker.
   2. disablePerformanceAntipatternChecker.
2. disablePerformanceAntipatternChecker flag doesn't match the name of the option in Xcode:
   1. Thread Performance Checker
3. The current xcscheme.diagnostic API only has positive flags but does not mention enable:
   1. address_sanitizer, thread_sanitizer.

In the end, I chose to start with the xcscheme.diagnostic API and follow the convention there:

xcschemes.diagnostics(
    main_thread_checker = False,
    thread_performance_checker = False,
)

which uses a positive flag upon until the xcscheme tool execution:

if !enablePerformanceAntipatternChecker {
    components.append(#"disablePerformanceAntipatternChecker = "YES""#)
}

Let me know if you want this done differently ?

[cerisier]

Sorry.. Should be good now.