Add wrappers for gdb and lldb when invoked from bazel

Usage:

$ bazel run --run_under $(realpath tools/bazel-gdb-wrapper.sh) //src/workerd/server:workerd -- \
    serve $(realpath /samples/helloworld_esm/config.capnp)

tools/bazel-gdb-wrapper.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+#
+# A wrapper script so workerd can be debugged with gdb, if invoked via bazel run.
+#
+# Example command-line invocation:
+#
+# bazel run -c dbg --run_under $(realpath tools/bazel-gdb-wrapper.sh) \
+#   //src/workerd/server:workerd -- serve samples/helloworld_esm/config.capnp
+#
+
+set -euo pipefail
+
+cd "${BUILD_WORKSPACE_DIRECTORY}"
+gdb --args "$@"

tools/bazel-lldb-wrapper.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+#
+# A wrapper script so workerd can be debugged with lldb, if invoked via bazel run.
+#
+# Example command-line invocation:
+#
+# bazel run -c dbg --spawn_strategy=local --features=oso_prefix_is_pwd --run_under \
+#   $(realpath tools/bazel-lldb-wrapper.sh) \
+#   //src/workerd/server:workerd -- serve samples/helloworld_esm/config.capnp
+#
+# NB the additional spawn_strategy and features flags are necessary on OS X per
+# https://github.com/bazelbuild/bazel/issues/6327.
+
+set -euo pipefail
+
+cd "${BUILD_WORKSPACE_DIRECTORY}"
+lldb -- "$@"