[F.Rq.] Memory copy/mirror finder

Not to be confused with #3738. This is about "manual" copies of structs that a game might use for various reasons. It may happen that one copy is the "real" one and all pokes/freezes should be directed at it, and I'm suggesting that we add a way to search for apparent copies of a known area in memory.
As it stands, you can use RAM Search for this, but only up to the selected word size, and you can't reference the known copy by address, you need to copy its value(s). You can also "Find" in the Hex Editor, but again can't reference a byte string whose location is known (see also #1653).

Start by reading the RAM Search and Hex Editor functionality described in the issue, including the related issue #1653. Define how a known address and memory range should be used to find apparent copies beyond the selected word size, and confirm that the result can identify the copy to target. Done means the proposed search is usable for manual struct mirrors without requiring copied values.