Rust: Vendor 3rdparty dependencies.

We've been observing some performance issues using crate_universe on CI.
Therefore, we're moving to vendor the auto-generated BUILD files
in our repository. This should provide a nice speed boost, while
getting rid of the complexity of the "rust cache" job we've been using
when we had a lot of git dependencies.

This PR includes a vendor script, and I'll put up a CI job internally
that runs that vendor script on Cargo.toml and Cargo.lock changes, to check
that the vendored files are in sync.

rust/ast-generator/BUILD.bazel

@@ -1,5 +1,5 @@
-load("@tree_sitter_extractors_deps//:defs.bzl", "aliases", "all_crate_deps")
 load("//misc/bazel:rust.bzl", "codeql_rust_binary")
+load("//misc/bazel/3rdparty/tree_sitter_extractors_deps:defs.bzl", "aliases", "all_crate_deps")
 
 codeql_rust_binary(
     name = "ast-generator",
@@ -14,8 +14,4 @@ codeql_rust_binary(
     ),
 )
 
-filegroup(
-    name = "manifest",
-    srcs = ["Cargo.toml"],
-    visibility = ["//rust:__subpackages__"],
-)
+exports_files(["Cargo.toml"])

rust/ast-generator/Cargo.toml

@@ -3,6 +3,7 @@ name = "ast-generator"
 version = "0.1.0"
 edition = "2021"
 
+# When updating these dependencies, run `misc/bazel/3rdparty/update_cargo_deps.sh`
 [dependencies]
 ungrammar = "1.16.1"
 proc-macro2 = "1.0.33"