[bazel] Add hermetic Android NDK C++ toolchain.

See //toolchain/README.md to understand how I arrived at this design.

This toolchain can be tested via the following Bazel invocations:

    $ bazel build //... --config=android-arm-hermetic
    $ bazel build //... --config=android-arm-hermetic-rbe
    $ bazel build //... --config=android-arm64-hermetic
    $ bazel build //... --config=android-arm64-hermetic-rbe

In a follow-up CL I will delete the non-hermetic toolchain that uses the `android_ndk_repository`[1] built-in Bazel rule, and I will update the skcms-Android-ARM-Bazel-Build-RBE and skcms-Android-ARM64-Bazel-Build-RBE tasks to use the hermetic toolchain.

[1] https://bazel.build/reference/be/android#android_ndk_repository

Bug: skia:12400
Change-Id: I917c65a64e5e6320842d25940b2ca5477073f577
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/528654
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Leandro Lovisolo <lovisolo@google.com>
23 files changed