[build] Add a script to *just* generate the compilation db (#30315)

tools/distrib/gen_db.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+# Copyright 2015 gRPC authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# change to root directory
+cd $(dirname $0)/../..
+REPO_ROOT=$(pwd)
+
+# grep targets with manual tag, which is not included in a result of bazel build using ...
+# let's get a list of them using query command and pass it to gen_compilation_database.py
+export MANUAL_TARGETS=$(bazel query 'attr("tags", "manual", tests(//test/cpp/...))' | grep -v _on_ios)
+
+# generate a clang compilation database for all C/C++ sources in the repo.
+tools/distrib/gen_compilation_database.py \
+  --include_headers \
+  --ignore_system_headers \
+  --dedup_targets \
+  "//:*" \
+  "//src/core/..." \
+  "//src/compiler/..." \
+  "//test/core/..." \
+  "//test/cpp/..." \
+  $MANUAL_TARGETS