Mapping Symbols: Rethinking for Efficiency

tl;dr

- Mapping symbols describe data in code and instruction sets transition (e.g. A32<=>T32).

- Pending LLVM integrated assembler patch that will eliminate almost all mapping symbols without breaking disassemblers https://github.com/llvm/llvm-project/pull/99718

- RISC-V ISA extension `$x<ISA>` (unimplemented yet) would raise question where the relocatable files are more heterogeneous.

- Mach-O LC_DATA_IN_CODE describes ranges.

- Compressed .strtab and .symtab might be beneficial.