core: Add "fake" dependency on Guava's failureaccess

This allows users to upgrade to newer versions of Guava without breaking
the build due to missing transitive dependencies. Without it, when
increasing the Guava version to 27.0+ you see errors like:

stub/src/main/java/io/grpc/stub/ClientCalls.java:487: error: cannot access InternalFutureFailureAccess
  private static final class GrpcFuture<RespT> extends AbstractFuture<RespT> {
                       ^
  class file for com.google.common.util.concurrent.internal.InternalFutureFailureAccess not found

Note that using a runtime_dep does not fix the compilation error.

Long-term we will want our users to migrate to
jvm_maven_import_external. However, if we use it ourselves, it will
effectively require our users to use it immediately themselves. It has
low penetration today, including lack of usage by tools like
johnynek/bazel-deps.

Fixes #5214

core/BUILD.bazel

@@ -7,6 +7,7 @@ java_library(
     deps = [
         "//context",
         "@com_google_code_findbugs_jsr305//jar",
+        "@com_google_guava_failureaccess//jar",  # future transitive dep of Guava. See #5214
         "@com_google_guava_guava//jar",
         "@com_google_j2objc_j2objc_annotations//jar",
     ],

repositories.bzl

@@ -11,6 +11,7 @@ def grpc_java_repositories(
         omit_com_google_code_gson = False,
         omit_com_google_errorprone_error_prone_annotations = False,
         omit_com_google_guava = False,
+        omit_com_google_guava_failureaccess = False,
         omit_com_google_j2objc_j2objc_annotations = False,
         omit_com_google_protobuf = False,
         omit_com_google_protobuf_java = False,
@@ -52,6 +53,8 @@ def grpc_java_repositories(
         com_google_errorprone_error_prone_annotations()
     if not omit_com_google_guava:
         com_google_guava()
+    if not omit_com_google_guava_failureaccess:
+        com_google_guava_failureaccess()
     if not omit_com_google_j2objc_j2objc_annotations:
         com_google_j2objc_j2objc_annotations()
     if not omit_com_google_protobuf:
@@ -177,6 +180,16 @@ def com_google_guava():
         licenses = ["notice"],  # Apache 2.0
     )
 
+def com_google_guava_failureaccess():
+    # Not needed until Guava 27.0, but including now to ease upgrading of users. See #5214
+    jvm_maven_import_external(
+        name = "com_google_guava_failureaccess",
+        artifact = "com.google.guava:failureaccess:1.0.1",
+        server_urls = ["http://central.maven.org/maven2"],
+        artifact_sha256 = "a171ee4c734dd2da837e4b16be9df4661afab72a41adaf31eb84dfdaf936ca26",
+        licenses = ["notice"],  # Apache 2.0
+    )
+
 def com_google_j2objc_j2objc_annotations():
     jvm_maven_import_external(
         name = "com_google_j2objc_j2objc_annotations",