Pin git dependencies in Cargo.toml #42027
Description
Instead of just pointing to a branch and relying on our Cargo.lock, we should pin git dependencies to a specific commit (or tag) in Cargo.toml.
This makes it much easier for third-party embedders to get the same dependency versions as servo has.
Medium to Long-term we should try to use releases from crates.io, but short term this seems like a solution that makes updating slightly more manual work for us, but makes it much easier for embedders.
See also feedback from slint-ui/slint#10491 (reply in thread)
Example fix:
[dependencies]
regex = { git = "https://github.com/rust-lang/regex.git", rev = "commit-hash" }