rust: handle modules with same crate_name

crate_name do not need to be unique. A library may depend on two
different versions of the same crate. Use the module name instead of the
crate name when indexing the modules for rust-project.json.

Test: SOONG_GEN_RUST_PROJECT=1 m nothing
Bug: 162896400
Change-Id: I8af9115b106fda2bed5b9fe96059cc29a33ac247