binexport: extract import / export symbols from BinExport file

The main argument for this is to take advantage of name demangling handled by the underlying disassembler (IDA, Ghidra, etc.). Optionally, add name demangling to capa's `ElfFeatureExtractor`.

Start by locating the BinExport parsing flow and capa's ElfFeatureExtractor. Determine how import and export symbols are represented in BinExport files and whether demangling can be reused from the underlying disassembler. Done means the requested symbols are extracted, with ElfFeatureExtractor demangling treated as an optional separate outcome.

Written by the indexing model from the issue text.