bazel syntax: break dependency on lib.events.Event

This change removes nearly all dependencies on lib.event.Event,
in preparation for reversing the lib.syntax->lib.event dependency.

SyntaxError is renamed to SyntaxError.Exception, and SyntaxError
itself is a simple event-like location+message type.

PiperOrigin-RevId: 304262913
diff --git a/src/test/java/com/google/devtools/build/lib/skylark/SkylarkRuleClassFunctionsTest.java b/src/test/java/com/google/devtools/build/lib/skylark/SkylarkRuleClassFunctionsTest.java
index 62cf58e..f653a64 100644
--- a/src/test/java/com/google/devtools/build/lib/skylark/SkylarkRuleClassFunctionsTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skylark/SkylarkRuleClassFunctionsTest.java
@@ -738,7 +738,7 @@
     Module module = thread.getGlobals();
     StarlarkFile file = EvalUtils.parseAndValidate(input, FileOptions.DEFAULT, module);
     if (!file.ok()) {
-      throw new SyntaxError(file.errors());
+      throw new SyntaxError.Exception(file.errors());
     }
     SkylarkImportLookupFunction.execAndExport(file, FAKE_LABEL, ev.getEventHandler(), thread);
   }