[Cards] Use Starlark macros. (material-components#8163)

Updates the BUILD file to use as many Starlark macros as possible. Makes
releasing easier.

Part of #8150

Author: Robert Moore

components/Cards/BUILD

@@ -22,17 +22,17 @@ load(
     "mdc_public_objc_library",
     "mdc_snapshot_objc_library",
     "mdc_snapshot_test",
+    "mdc_unit_test_objc_library",
     "mdc_unit_test_suite",
+    "mdc_unit_test_swift_library",
 )
-load("@build_bazel_rules_swift//swift:swift.bzl", "swift_library")
 
 licenses(["notice"])  # Apache 2.0
 
 mdc_public_objc_library(
     name = "Cards",
     sdk_frameworks = [
         "CoreGraphics",
-        "UIKit",
     ],
     visibility = ["//visibility:public"],
     deps = [
@@ -82,17 +82,11 @@ mdc_extension_objc_library(
     ],
 )
 
-swift_library(
+mdc_unit_test_swift_library(
     name = "unit_test_swift_sources",
-    srcs = glob([
-        "tests/unit/*.swift",
+    extra_srcs = glob([
         "tests/unit/Theming/*.swift",
     ]),
-    copts = [
-        "-swift-version",
-        "4.2",
-    ],
-    visibility = ["//visibility:private"],
     deps = [
         ":Cards",
         ":ColorThemer",
@@ -101,18 +95,8 @@ swift_library(
     ],
 )
 
-mdc_objc_library(
+mdc_unit_test_objc_library(
     name = "unit_test_sources",
-    testonly = 1,
-    srcs = native.glob([
-        "tests/unit/*.m",
-        "tests/unit/*.h",
-    ]),
-    sdk_frameworks = [
-        "UIKit",
-        "XCTest",
-    ],
-    visibility = ["//visibility:private"],
     deps = [
         ":Cards",
         "//components/private/Icons/icons/ic_info",