Allow to customize separator for messaging destinations

In order to be able to use separators like "." (used by default
by most broker relays) instead of "/" for destination patterns
handling, the PathMatcher used in spring-messaging can now
be customized easily thanks to XML websocket namespace
or JavaConfig.

AntPathMatcher has been updated in order to use the configured path
separator instead of an hardcoded "/" for path concatenation.
Extension handling is now disabled when the "." separator is configured.

Issue: SPR-11660