Improve ELF symbolization for .plt stubs

ELF binaries often contain named imported-function trampolines in the `.plt`, but today those addresses can show up in profiles as generic synthesized names like `fun_XXXX` because the stubs have unwind coverage without matching symbols at the stub addresses. This improvement makes symbolization recognize PLT stubs and assign meaningful names derived from the dynamic relocations, so the PLT resolver appears as `<PLT header>` and individual entries appear as names like `strcmp@plt` or `printf@plt`, making stacks much easier to read.