Only allow alphanumerical characters, '-' and '_' in event trigger names

This should help in preventing silly typos like "on foo:"

Test: atest CtsInitTestCases
Test: builds
Bug: 135984674
Change-Id: I6e4e18970e957d25dea9f557f0d31a759fbe6150
diff --git a/init/init_test.cpp b/init/init_test.cpp
index 315d584..9f63e4f 100644
--- a/init/init_test.cpp
+++ b/init/init_test.cpp
@@ -93,6 +93,26 @@
     EXPECT_TRUE(expect_true);
 }
 
+TEST(init, WrongEventTrigger) {
+    std::string init_script =
+            R"init(
+on boot:
+pass_test
+)init";
+
+    TemporaryFile tf;
+    ASSERT_TRUE(tf.fd != -1);
+    ASSERT_TRUE(android::base::WriteStringToFd(init_script, tf.fd));
+
+    ActionManager am;
+
+    Parser parser;
+    parser.AddSectionParser("on", std::make_unique<ActionParser>(&am, nullptr));
+
+    ASSERT_TRUE(parser.ParseConfig(tf.path));
+    ASSERT_EQ(1u, parser.parse_error_count());
+}
+
 TEST(init, EventTriggerOrder) {
     std::string init_script =
         R"init(