Cherry-pick 303205@main (bb3b3f72e7e2). https://bugs.webkit.org/show_bug.cgi?id=302649

    [GLib] Drop WTF_ALLOW_UNSAFE_BUFFER_USAGE in SocketConnection::readMessage()
    https://bugs.webkit.org/show_bug.cgi?id=302649

    Reviewed by Michael Catanzaro.

    Use spans over the received message buffer to parse the different
    elements of the message, advancing over the input idiomatically using
    consumeAndReinterpretCastTo(), consumeSpan(), and skip().

    Note that the message body size is always extended from uint32_t to a
    size_t, and that the value is never modified and therefore it does not
    need to be Checked<size_t> because there is no arithmetic performed on
    it.

    While at it, check and detect for messages missing the message name
    delimiter, too short messages, or messages larger than 512 MiB (assuming
    that no message will ever need to be that big). When an invalid message
    is detected, use the new didReceiveInvalidMessage() helper to report it,
    close the connection, and discard the read buffer.

    * Source/WTF/wtf/glib/SocketConnection.cpp:
    (WTF::SocketConnection::didReceiveInvalidMessage): Added.
    (WTF::SocketConnection::readMessage): Modernize to use spans and add
    additional sanity checks.
    * Source/WTF/wtf/glib/SocketConnection.h: Added didReceiveInvalidMessage
    declaration.

    Canonical link: https://commits.webkit.org/303205@main

Canonical link: https://commits.webkit.org/290945.412@webkitglib/2.48