find bazel-related files and add them to bazel.list and ninja deps

This retriggers soong_build whenever a new bzl, WORKSPACE, or
BUILD.bazel file is changed or added.

Test: Manually verified on bionic/libc genrules with manual changes to
related BUILD/bzl/WORKSPACE files -- these all retrigger builds.
Test: Updated finder_test.go

Change-Id: I634384f88781a6b6db32f5d6bf9c07e179e14c39