Deprecate JMX Management Applets for Removal

Deprecate the Java Management Extension (JMX) Management Applet (m-let) feature for removal in a future release.

M-lets, which were inspired by applets, are irrelevant to modern applications. There is no evidence that m-lets were ever widely used: there are no bug reports, and no evidence of discussion in public forums. There is no significant interest in developing modern applications that use m-lets. This deprecation will have no impact on users of other JMX features, the JDK's built-in instrumentation, or any of the observability tools.

We will terminally deprecate the following classes, by annotating them with @Deprecated(forRemoval=true):
javax.management.loading.MLet
javax.management.loading.MLetContent
javax.management.loading.PrivateMLet
javax.management.loading.MLetMBean