Add support for dynamic symbols when DYNAMIC segment is missing

[nsavoire]

Symbolic currently relies on DYNAMIC segment to locate and parse dynamic symbols.
This works for full executables but not for debug information extracted with objcopy --only-keep-debug where we have added back dynamic symbol sections (.dynsym / .dynstr), because in those files, DYNAMIC segment is stripped.
This PR adds the ability to use section headers to locate .dynsym and .dynstr sections when DYNAMIC segment cannot be used.

[Copilot]

Pull Request Overview

This PR enables parsing of dynamic symbols and their string table from section headers when the PT_DYNAMIC segment is absent, falling back to PT_DYNAMIC only if needed.

• Initialize dynsyms and dynstrtab earlier to a known default state
• Add parsing of .dynsym/.dynstr via SHT_DYNSYM section
• Introduce fallback logic: use DYNAMIC segment only if section-based tables are empty

Comments suppressed due to low confidence (1)

symbolic-debuginfo/src/elf.rs:245

• Add unit tests to verify the new fallback behavior: parsing .dynsym/.dynstr sections in the absence of a PT_DYNAMIC segment, ensuring correct symbol resolution for debug-only ELF files.

if obj.dynstrtab.len() == 0 {

[nsavoire]

Some open questions:

• How should we name this new version ? Should we use a new branch ? (Since the current version is identified by this branch, not a tag)
• Should we also update to a newer symbolic version? (I noticed this change that could be interesting)

[Copilot]

Pull Request Overview

This PR adds a fallback mechanism to locate and parse dynamic symbols using section headers when the DYNAMIC segment is missing, targeting debug information files produced by objcopy.

• Added fallback logic in elf.rs to iterate over section headers and parse .dynsym and .dynstr sections when obj.dynsyms is empty
• Adjusted data parsing to support files without a DYNAMIC segment

[Copilot]

After successfully parsing the dynamic symbol table and string table, consider breaking out of the loop to prevent potential overwrites if multiple SHT_DYNSYM sections are present.

Suggested change

	obj.dynstrtab = return_partial_on_err!(get_strtab(&obj.section_headers, shdr.sh_link as usize));
	obj.dynstrtab = return_partial_on_err!(get_strtab(&obj.section_headers, shdr.sh_link as usize));
	break;