Support changes to `getelementptr` instruction in LLVM 19

[RyanGlScott]

If you attempt to compile the following LLVM bitcode using llvm-as-19.1.0 and then parse it using llvm-pretty-bc-parser, it will fail:

%struct.RT = type { i8, [10 x [20 x i32]], i8 }
%struct.ST = type { i32, double, %struct.RT }

define ptr @foo(ptr %s) {
entry:
  %arrayidx = getelementptr inbounds %struct.ST, ptr %s, i64 1, i32 2, i32 1, i64 5, i64 13
  ret ptr %arrayidx
}

λ> parseBitCodeFromFile "test.bc"
Left (Error {errContext = ["FUNC_CODE_INST_GEP","@foo","FUNCTION_BLOCK","FUNCTION_BLOCK_ID","value symbol table","MODULE_BLOCK","Bitstream"], errMessage = "parseField: unable to parse record field 0 of record Record {recordCode = 43, recordFields = [FieldFixed (BitString {bsLength = NumBits 3, bsData = 3}),FieldFixed (BitString {bsLength = NumBits 4, bsData = 10}),FieldVBR (BitString {bsLength = NumBits 5, bsData = 6}),FieldVBR (BitString {bsLength = NumBits 5, bsData = 5}),FieldVBR (BitString {bsLength = NumBits 5, bsData = 4}),FieldVBR (BitString {bsLength = NumBits 5, bsData = 3}),FieldVBR (BitString {bsLength = NumBits 5, bsData = 2}),FieldVBR (BitString {bsLength = NumBits 5, bsData = 1})]}"})

I'm not entirely sure what is going on yet, but I suspect it is related to the changes brought about by this proposal. (See also #278, which is about constant getelementptr expressions rather than getelementptr instructions.)