[Courgette] Clean up Disassembler; fix ELF Memory leaks.

Cleaning up code surrounding Disassembler:
- Extract AddressTranslator interface to be used across subclasses.
- Use FileOffset = size_t by context.
- Detailed comments & TODOs in DisassemblerElf32ARM.
- Fix DisassemblerElf32ARM memory leaks.
- Lots of superficial stylistic changes.

Except for AddressTranslator routines and unit tests, shying away
from control flow and logic changes.

BUG=579206

Review URL: https://codereview.chromium.org/1676683002

Cr-Commit-Position: refs/heads/master@{#380881}
19 files changed