[llvm] [AArch64] Reland merge index address with large offset into base address (PR #79951)

[David Green via llvm-commits]

davemgreen wrote:

> Only LDRBBroX is supported for the first time.

I think all the instructions from https://github.com/llvm/llvm-project/pull/75343/commits/f5687636415969e6d945659a0b78734abdfb0f06 should be added. Else we miss bugs due to a lack of test coverage.

https://github.com/llvm/llvm-project/pull/79951