Switch everything to platforms

This patch switches the codebase over from using the "cpu"
mechanism to using bazel platforms. See
https://docs.bazel.build/versions/master/platforms.html for some more
information.

Most of the substantial changes are in //tools. Instead of using
`cc_toolchain_suite` rules, we now use regular `toolchain` rules that
are registered in the WORKSPACE. That also means that bazel now uses
the target platform to select the compiler.

All --cpu=* arguments should now be --config=* arguments. For example,
`--cpu=roborio` should now be `--config=roborio`. The CI script and
all documentation has been updated to reflect that.

The remainder of the changes revolve around tagging all targets with
`target_compatible_with`.  The old mechanism allowed us to specify
repo-wide defaults. The new mechanism does not. That means every
target that didn't have any compatibility specified, now requires
compatibility with `@platforms//os:linux`.

I used buildozer for the vast majority of `target_compatible_with`
changes. buildozer automatically buildifies any BUILD files it
touches. That means this patch also contains a few non-functional
changes that I was too lazy to remove.

Change-Id: I66d6e6ad9161520ee397597cdb492585820a3acd
diff --git a/y2020/vision/BUILD b/y2020/vision/BUILD
index aaad085..a58ed8c 100644
--- a/y2020/vision/BUILD
+++ b/y2020/vision/BUILD
@@ -5,6 +5,7 @@
     name = "vision_fbs",
     srcs = ["vision.fbs"],
     gen_reflections = 1,
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//y2020:__subpackages__"],
 )
 
@@ -16,6 +17,7 @@
     hdrs = [
         "v4l2_reader.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//y2020:__subpackages__"],
     deps = [
         ":vision_fbs",
@@ -34,10 +36,7 @@
     data = [
         "//y2020:config",
     ],
-    restricted_to = [
-        "//tools:k8",
-        "//tools:armhf-debian",
-    ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//y2020:__subpackages__"],
     deps = [
         ":v4l2_reader",
@@ -57,6 +56,7 @@
 flatbuffer_ts_library(
     name = "vision_ts_fbs",
     srcs = ["vision.fbs"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//y2020:__subpackages__"],
 )
 
@@ -68,10 +68,7 @@
     data = [
         "//y2020:config",
     ],
-    restricted_to = [
-        "//tools:k8",
-        "//tools:armhf-debian",
-    ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//y2020:__subpackages__"],
     deps = [
         ":vision_fbs",
@@ -90,10 +87,7 @@
     data = [
         "//y2020:config",
     ],
-    restricted_to = [
-        "//tools:k8",
-        "//tools:armhf-debian",
-    ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//y2020:__subpackages__"],
     deps = [
         ":vision_fbs",
@@ -117,10 +111,7 @@
     data = [
         "//y2020:config",
     ],
-    restricted_to = [
-        "//tools:k8",
-        "//tools:armhf-debian",
-    ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//y2020:__subpackages__"],
     deps = [
         ":vision_fbs",