debuginfo: Generate cross-crate unique type identifiers for debuginfo types.

With this change, rustc creates a unique type identifier for types in debuginfo. These type identifiers are used by LLVM to correctly handle link-time-optimization scenarios but also help rustc with dealing with inlining from other crates. For more information, see the documentation block at the top of librustc/middle/trans/debuginfo.rs.

Fixes #13681.