pw_tokenizer: Tokenization options for proto

- Add a proto option for marking a field as tokenized.
- Create tools for automatically detokenizing protos with tokenized
  fields.
- Add missing inputs (ELF files for tests) to pw_tokenizer.
- Copy inputs to the out directory for generated packages.

Change-Id: If724cdb5e24ff3a86e89690806aa77fd4e7fdbe9
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/47741
Commit-Queue: Wyatt Hepler <hepler@google.com>
Pigweed-Auto-Submit: Wyatt Hepler <hepler@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
Reviewed-by: Ewout van Bekkum <ewout@google.com>