cargo_embargo: Implement rules.mk generation

Implement the generation of Trusty makefile rules from cargo embargo.
This change adds all the messy logic to generate the actual rules file
contents.

Test: m cargo_embargo
Test: cargo_embargo generate cargo_embargo.json (and inspect resulting rules)
Bug: 307615277
Change-Id: I4fa301cfd238b180fa584e064908f9897aeb0624
1 file changed