* update win RBE docker image and toolchain
and switch win RBE builds to using it.
* delete legacy RBE windows toolchain config
* switching to VS2019 makes #28544 obsolete
* Remove the toolchains //third_party/toolchains:local and //third_party/toolchains:local_large.
* Remove the platforms :rbe_ubuntu1604, :rbe_ubuntu1604_large, :local and :local_large.
* No longer inherit from @rbe_default//config:platform but instead use it directly. It is now the only non-windows platform.
* When creating @rbe_default//config:platform directly with rbe_autoconfig, set dockerAddCapabilities and dockerPrivileged directly in the exec_properties field. No need to set dockerNetwork to "off" and dockerSiblingContainers to false since these are the defaults.
* Also set gceMachineType = "n1-highmem-2" on the default platform. This value can be overridden by specific targets that want to use LARGE_MACHINE.
* Use create_exec_properties_dict where appropriate.
* Use custom_exec_properties to define LARGE_MACHINE.
I wasn't able to test thoroughly that this PR does not break any existing targets. I was not able to run anything on windows/mac and I also don't have access to gRPC's RBE setup.
This should fix Bazel Basic Tests for Python (Local) and other
local CI runs that are now failing.
I also have a plan to fix Bazel RBE Opt C/C++.
Bazel RBE UBSAN C/C++ might need to wait for gRPC to upgrade to
using 0.23.0