[FEATURE] Disable RealURL with register

RealURL can be disabled for single links by setting
the tx_realurl_disable register to TRUE.

Resolves: #53033
Change-Id: I84ac224fe3340bce193d4c3c70d8e1c8e7d6fc7c
[BUGFIX] Override path for subpages

If the checkbox for tx_realurl_pathoverride is enabled
the path of the subpages is now also overwritten.

Resolves: #54764
Change-Id: Ic1a897b468f44bfae2d8e2148f832b5980729a20
[BUGFIX] No path override for mount points

When generating RealURLs for a page inside a mount point the whole
page path will never be overridden because otherwise the mount point
path will be lost.

Resolves: #57960
Change-Id: I490577fc7efbbfce0a173382c32232ecff267f54