[lld] [llvm] [Object,ELFType] Rename TargetEndianness to Endianness (PR #86604)

[Alexander Richardson via llvm-commits]

arichardson wrote:

I guess the slightly shorter version could be `ByteOrder` but endianess is probably better. I agree that the Target prefix does not make any sense since it's the endianess for a given elf type and is unrelated to host/target.

https://github.com/llvm/llvm-project/pull/86604