[llvm-objdump] --disassemble-symbols doesn't account for ELF symbol size

Elf Symbols often have a specific size. This size (when nonzero) is not taken into account by `--disassemble-symbols=`

This makes it hard to disassemble a single function, if that function has e.g. local symbols. This can happen when disassembling a relocatable object. The disassembly will stop at the first local symbol, rather than disassembling the encoded size of the function.

Of course, if the size is zero, we have to treat the size as unknown, and stopping on the next symbol mostly makes sense - though I don't know whether we should take into account the symbol binding, and maybe skip local symbols.

This comment implies this is intended behaviour, but I think it would be better if it wasn't the behaviour

https://github.com/llvm/llvm-project/blob/0cdebdaf59d20f34158d97d193381e95a0ba90b0/llvm/tools/llvm-objdump/llvm-objdump.cpp#L2135-L2136

Start in llvm/tools/llvm-objdump/llvm-objdump.cpp at lines 2135-2136 and inspect how --disassemble-symbols determines its stopping point. Reproduce the behavior with a relocatable object containing local symbols, then verify that a nonzero ELF symbol size is honored while the zero-size case follows an agreed stopping rule.

Written by the indexing model from the issue text.