Rust: fetch ungram and rust-analyzer code instead of checking it in

* The ungram file is now taken from the rust-analyzer dependencies
  pulled in by bazel
* the grammar parsing code is not published, so it must be taken
  directly from rust-analyzer code. That part should be less prone to be
  updated than the ungram file, so it does not necessarily need to be
  in sync with the rust-analyzer version is used elsewhere.
* both need some patches. The former is patched during build, the latter
  during loading in `MODULE.bazel`.

rust/codegen/BUILD.bazel

@@ -3,6 +3,7 @@ load("@rules_shell//shell:sh_binary.bzl", "sh_binary")
 
 _args = [
     "//rust/ast-generator",
+    "//rust/ast-generator:ungram",
     "//rust/ast-generator:Cargo.toml",
     "//misc/codegen",
     "//rust:codegen-conf",

rust/codegen/codegen.sh

@@ -5,10 +5,11 @@ set -eu
 source misc/bazel/runfiles.sh 2>/dev/null || source external/ql+/misc/bazel/runfiles.sh
 
 ast_generator="$(rlocation "$1")"
-ast_generator_manifest="$(rlocation "$2")"
-codegen="$(rlocation "$3")"
-codegen_conf="$(rlocation "$4")"
-shift 4
+grammar_file="$(rlocation "$2")"
+ast_generator_manifest="$(rlocation "$3")"
+codegen="$(rlocation "$4")"
+codegen_conf="$(rlocation "$5")"
+shift 5
 
-CARGO_MANIFEST_DIR="$(dirname "$ast_generator_manifest")" "$ast_generator"
+CARGO_MANIFEST_DIR="$(dirname "$ast_generator_manifest")" "$ast_generator" "$grammar_file"
 "$codegen" --configuration-file="$codegen_conf" "$@"