Add Bazel build

[armandomontanez]

Adds a Bazel build for Picotool. The Bazel build comes with a few perks:

1. You don't need to set PICO_SDK_PATH. It's still possible to locally override with --override_module=pico-sdk=/path/to/pico-sdk.
2. Libusb is built from source. The version to use can be controlled in dependent projects by using rules_libusb version constraints.
3. Windows works out of the box with just MSVC.