Simplify WORKSPACE.bzlmod and add CI test for Bzlmod

- All workspace suffix are removed from WORKSPACE.bzlmod, since we get
  all dependencies and toolchains from Bzlmod.
- Added build:bzlmod bazelrc section, we have to override two flags to
  make sure toolchains are picked up correctly.
- Added zstd-jni as dependency
- Added postsubmit_bzlmod.yml for testing the Bzlmod build.

Tested at https://buildkite.com/bazel/bazel-bazel-with-bzlmod/builds/3

Closes #14312.

PiperOrigin-RevId: 411855954

.bazelci/postsubmit_bzlmod.yml

@@ -0,0 +1,38 @@
+---
+tasks:
+  centos7_java11_devtoolset10:
+    build_flags:
+      - "--config=bzlmod"
+    build_targets:
+      - "//src:bazel_nojdk"
+  ubuntu1804:
+    build_flags:
+      - "--config=bzlmod"
+    build_targets:
+      - "//src:bazel_nojdk"
+  ubuntu1804_clang:
+    platform: ubuntu1804
+    environment:
+      CC: clang
+      CC_CONFIGURE_DEBUG: 1
+    name: "Clang"
+    build_flags:
+      - "--config=bzlmod"
+    build_targets:
+      - "//src:bazel_nojdk"
+  ubuntu2004:
+    build_flags:
+      - "--config=bzlmod"
+    build_targets:
+      - "//src:bazel_nojdk"
+  macos:
+    xcode_version: "13.0"
+    build_flags:
+      - "--config=bzlmod"
+    build_targets:
+      - "//src:bazel_nojdk"
+  windows:
+    build_flags:
+      - "--config=bzlmod"
+    build_targets:
+      - "//src:bazel_nojdk"

.bazelrc

@@ -29,5 +29,11 @@ build:remote --config=ubuntu1804_java11
 
 build:macos --macos_minimum_os=10.10
 
+# Enable Bzlmod
+build:bzlmod --experimental_enable_bzlmod
+# TODO(pcloudy): The following should be removed after fixing https://github.com/bazelbuild/bazel/issues/14279
+build:bzlmod --crosstool_top=@rules_cc.0.0.1.cc_configure.local_config_cc//:toolchain
+build:bzlmod --xcode_version_config=@rules_cc.0.0.1.cc_configure.local_config_xcode//:host_xcodes
+
 # User-specific .bazelrc
 try-import user.bazelrc

MODULE.bazel

@@ -13,6 +13,7 @@ bazel_dep(name = "grpc", version = "1.41.0", repo_name = "com_github_grpc_grpc")
 bazel_dep(name = "platforms", version = "0.0.4")
 bazel_dep(name = "rules_pkg", version = "0.5.1")
 bazel_dep(name = "stardoc", version = "0.5.0", repo_name = "io_bazel_skydoc")
+bazel_dep(name = "zstd-jni", version = "1.5.0-4")
 
 # TODO(pcloudy): Add remoteapis and googleapis as Bazel modules in the BCR.
 bazel_dep(name = "remoteapis", version = "")
@@ -27,10 +28,7 @@ local_path_override(
 )
 
 # The following are required when building without WORKSPACE SUFFIX
-# TODO(pcloudy): Make building Bazel work without WORKSPACE SUFFIX.
-# This requires migrating all dependencies and toolchain registration defined in
-# WORKSPACE to their corresponding Bazel modules. Eg. remote jdks, java tools
-# and java toolchain registrations all should be moved to rules_java.
 bazel_dep(name = "rules_cc", version = "0.0.1")
-bazel_dep(name = "rules_java", version = "4.0.0")
+bazel_dep(name = "rules_python", version = "0.4.0")
+bazel_dep(name = "rules_java", version = "5.0.0")
 bazel_dep(name = "rules_proto", version = "4.0.0")