Avoid building the non-test file group in :all. (#3191)

This file group exists to allow a `genquery` rule and a Python test to
verify our non-test dependency graph. We don't actually need to build
the binaries in the file group as part of that. The `genquery` rule
seems to do the right thing -- building it directly doesn't cause the
binaries in the group to be built. But without a manual tag, the group
itself is part of `:all` and thus part of `//...` and part of the rules
that will be built even with PR #3106. A consequence is that any change
to the toolchain causes several other binaries to be built as well
because this file group is in the impacted set. Making it manual should
avoid all of this, and without breaking the actual use from `genquery`.

For example, before this change, in a fully cached build after a `bazel
clean`:
```
> bazel test //bazel/check_deps:all
INFO: Invocation ID: 2d83ebee-4c00-425d-be33-23f42b079614
INFO: Analyzed 3 targets (103 packages loaded, 7137 targets configured).
INFO: Found 2 targets and 1 test target...
INFO: Elapsed time: 4.081s, Critical Path: 2.61s
INFO: 3111 processes: 2796 disk cache hit, 315 internal.
INFO: Build completed successfully, 3111 total actions
```

After this change:
```
> bazel test //bazel/check_deps:al
INFO: Invocation ID: c94089e8-a420-4d3c-9902-134e6b55b297
INFO: Analyzed 2 targets (92 packages loaded, 568 targets configured).
INFO: Found 1 target and 1 test target...
INFO: Elapsed time: 0.700s, Critical Path: 0.01s
INFO: 7 processes: 2 disk cache hit, 5 internal.
INFO: Build completed successfully, 7 total actions
```

While here, re-generate the file group, and fix several issues it
uncovers: mark test utilities as `testonly` and update our LLVM package
allowlist to include `clangd`'s package.

bazel/check_deps/BUILD

@@ -15,11 +15,13 @@ filegroup(
     data = [
         "//explorer",
         "//installers/local:carbon",
+        "//language_server",
         "//migrate_cpp:rewriter",
         "//migrate_cpp/cpp_refactoring",
-        "//toolchain/diagnostics:null_diagnostics",
         "//toolchain/driver:carbon",
+        "//utils/treesitter",
     ],
+    tags = ["manual"],
 )
 
 genquery(

bazel/check_deps/check_non_test_cc_deps.py

@@ -42,7 +42,7 @@ for dep in deps:
 
         # Other packages in the LLVM project shouldn't be accidentally used
         # in Carbon. We can expand the above list if use cases emerge.
-        if package not in ("llvm", "lld", "clang"):
+        if package not in ("llvm", "lld", "clang", "clang-tools-extra/clangd"):
             sys.exit(
                 "ERROR: unexpected dependency into the LLVM project: %s" % dep
             )

common/BUILD

@@ -71,6 +71,7 @@ cc_library(
 
 cc_library(
     name = "enum_base_test_def",
+    testonly = 1,
     textual_hdrs = ["enum_base_test.def"],
 )
 

language_server/BUILD

@@ -5,6 +5,8 @@
 load("@rules_cc//cc:defs.bzl", "cc_binary")
 
 package(default_visibility = [
+    "//bazel/check_deps:__pkg__",
+    "//installers:__subpackages__",
     "//language_server:__subpackages__",
 ])
 

utils/treesitter/BUILD

@@ -5,6 +5,11 @@
 load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_test")
 load("@rules_tree_sitter//tree_sitter:tree_sitter.bzl", "tree_sitter_cc_library")
 
+package(default_visibility = [
+    "//bazel/check_deps:__pkg__",
+    "//installers:__subpackages__",
+])
+
 tree_sitter_cc_library(
     name = "treesitter",
     srcs = ["src/scanner.c"],
@@ -13,6 +18,7 @@ tree_sitter_cc_library(
 
 cc_binary(
     name = "test_runner",
+    testonly = 1,
     srcs = ["test_runner.cpp"],
     deps = [
         ":treesitter",