Apply some message checks from the .cpp WebBackFowardList to the Swift one

rdar://189219104
https://bugs.webkit.org/show_bug.cgi?id=326397

Reviewed by Abrar Rahman Protyasha.

These are the checks added in 320667@main

* Source/WebKit/UIProcess/WebBackForwardList.cpp:
(frameStateChildCount):
(frameStateChildAtIndex):
(maxFrameStateDepthForMessageCheck):
* Source/WebKit/UIProcess/WebBackForwardList.swift:
(Direction.messageCheckItemURLs(_:process:)): Deleted.
* Source/WebKit/UIProcess/WebBackForwardListSwiftUtilities.h:

Canonical link: https://commits.webkit.org/322782@main