Define Bazel coverage config

Define configuration options for collecting coverage data with Bazel.

The coverage command for Bazel is fairly fragile and many configurations
do not work [1,2]. The `--javabase` option is set as suggested in this
bug report[3]. Coverage has been manually tested with GCC 7 on Ubuntu
18.04.

[1]: bazelbuild/bazel#9406
[2]: bazelbuild/bazel#10457
[3]: bazelbuild/bazel#7953

.bazelrc

@@ -9,3 +9,9 @@ test --build_tests_only
 test --test_output=errors
 test --test_summary=detailed
 test --action_env='GTEST_COLOR=1'
+
+coverage -c dbg
+coverage --instrumentation_filter=''
+coverage --javabase=@bazel_tools//tools/jdk:remote_jdk11
+coverage --combined_report=lcov
+coverage --coverage_report_generator=@bazel_tools//tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator:Main