bp2build: Handle target.linux

Also refactor target.bionic to be handled not as its own configuration
axis, but instead to be grouped into os selects handling.

This allows us to remove libbase and its dependencies from the bp2build
denylist.

Test: mixed_droid.sh CI
Change-Id: I92f30074d286306207653fe37589835ae3db16c4

bp2build/cc_library_static_conversion_test.go

@@ -1382,7 +1382,8 @@ cc_library_static {
 		expectedBazelTargets: []string{`cc_library_static(
     name = "target_bionic",
     system_dynamic_deps = select({
-        "//build/bazel/platforms/os:bionic": [":libc"],
+        "//build/bazel/platforms/os:android": [":libc"],
+        "//build/bazel/platforms/os:linux_bionic": [":libc"],
         "//conditions:default": [],
     }),
 )`},