use more Rc in the part of resolver that gets cloned a lot
use more Rc in the part of resolver that gets cloned a lot

In a test on https://github.com/rust-lang/cargo/issues/4810#issuecomment-357553286
Before we got to 1700000 ticks in ~(82 to 97) sec
After we got to 1700000 ticks in ~(63 to 67) sec

vojtechkral/cargo,vojtechkral/cargo,tshepang/cargo,vojtechkral/cargo,tshepang/cargo,rustyhorde/cargo,rustyhorde/cargo,rust-lang/cargo,rust-lang/cargo,eminence/cargo,tsurai/cargo,nipunn1313/cargo,nipunn1313/cargo,eminence/cargo,eminence/cargo,nipunn1313/cargo,tsurai/cargo,tsurai/cargo,rust-lang/cargo,tsurai/cargo,rust-lang/cargo,vojtechkral/cargo,rustyhorde/cargo,tshepang/cargo,rustyhorde/cargo,tshepang/cargo,tsurai/cargo,eminence/cargo,nipunn1313/cargo