Implement support for resource_sets API in bazel-common

[arunkumar9t2]

This PR implements support for resource_sets API introduced in grab/grab-bazel-common#165.

This is done by mapping AGP's AndroidSourceSet to newly added BazelSourceSet. During mapping, existence of the directories are checked for.

After this source, Gradle like variant declaration can be closely mimicked as below and resources, manifest and assets will be merged before actual build begins.

android_binary(
    name = "android_binary_sample",
    srcs = glob([
        "src/main/java/**/*.kt",
    ]),
    custom_package = "com.grab.test",
    manifest = "src/main/AndroidManifest.xml",
    resource_sets = {
        "flavor": {
            "res": "src/flavor/res",
            "manifest": "src/flavor/AndroidManifest.xml",
            "assets": "src/flavor/assets",
        },
        "main": {
            "res": "src/main/res",
            "manifest": "src/main/AndroidManifest.xml",
            "assets": "src/main/assets",
        },
    },
)