[Courgette] Reduce AssemblyProgram to reduce Courgette-apply RAM floor and disk churn.

This is the main CL of the AssemblyProgram reduction effort, which makes
Disassembler emit instructions directly to EncodedProgram, and bypass
AssemblyProgram, which becomes a holder of LabelManager and Label
Annotation. Another big change is that Disassembler usage is exposed to
high-level flows (rather than having it hidden inside
ParseDetectedExecutable*()). Details:

- Remove ParseDetectedExecutable*() and expose DetectDisassembler().
- AssemblyProgram: Remove:
  - Entire Instruction class hierarchy.
  - Allocated instruction in the heap (including preallocated DEFBYTE
    instances).
  - enum OP {}, which duplicates EncodedProgram::OP.
  - InstructionVector of pointers, which takes 100's of MB on disk.
  - Encode() interface.
- AssemblyProgram: Add:
  - AnnotateLabels() to generate Label Annotation directly from a
    generator (injected by Disassembler), using LabelReceptor template
    class for counting and storage.
  - PrepareEncodedProgram() to inject data needed (e.g., Label) to
    EncodedProgram.
- Disassembler: Disassemble() is split into CreateProgram() and
  DisassembleAndEncode().
- EncodedProgram: Old AssemblyProgram::Encode() code now moved to
  InstructionStoreReceptor. New GenerateInstruction() is added to
  receive generator from Disassemblyprogram.
- CourgetteFlow: Disassembler explicitly managed:
  - Remove ReadAssemblyProgramFromBuffer().
  - Add ReadDisassemblerFromBuffer().
  - Add CreateEncodedProgramFromDisassemblerAndAssemblyProgram().
- High-level flows in courgette_tool.cc, patch_generator_x86_32.h,
  patcher_x86_32.h: Using new more complex flow that involves
  Disassembler; using ASCII graphics in comment to illustrate.
- Unit tests updates.

Documentation update will be done in a follow-up.

BUG=660980

Review-Url: https://codereview.chromium.org/2854113002
Cr-Commit-Position: refs/heads/master@{#472907}

• courgette/adjustment_method_unittest.cc[diff]
• courgette/assembly_program.cc[diff]
• courgette/assembly_program.h[diff]
• courgette/courgette_flow.cc[diff]
• courgette/courgette_flow.h[diff]
• courgette/courgette_tool.cc[diff]
• courgette/disassembler.cc[diff]
• courgette/disassembler.h[diff]
• courgette/disassembler_elf_32_x86_unittest.cc[diff]
• courgette/encode_decode_unittest.cc[diff]
• courgette/encoded_program.cc[diff]
• courgette/encoded_program.h[diff]
• courgette/encoded_program_fuzz_unittest.cc[diff]
• courgette/instruction_utils.h[diff]
• courgette/patch_generator_x86_32.h[diff]
• courgette/patcher_x86_32.h[diff]
• courgette/program_detector.cc[diff]
• courgette/program_detector.h[diff]
• testing/libfuzzer/fuzzers/courgette_fuzzer.cc[diff]