[GR-63494] [GR-63728] Simplify the safepoint code and only enable recurring callback support on demand.

[graalvmbot]

This PR disables recurring callback support by default. Recurring callbacks are a rarely used feature, that comes with a performance cost. If this feature is needed, please explicitly enable it via -H:+SupportRecurringCallback at image build-time.

PR contains 4 commits and each commit can be reviewed on its own:

• refactored the recurring callback support (see RecurringCallbackSupport and ThreadingSupportImpl)
• changed the default value of -H:SupportRecurringCallback to false
• simplified the safepoint code
• renamings and cleanups