compiler: check emitted event names

Check that all `Notify` invocations in source correspond to some event
in manifest.
Helpful for typos such as `transfer` instead of `Transfer`.

cli/testdata/invalid3/invalid.go

@@ -0,0 +1,21 @@
+// invalid is an example of contract which doesn't pass event check.
+package invalid3
+
+import (
+	"github.com/nspcc-dev/neo-go/pkg/interop"
+	"github.com/nspcc-dev/neo-go/pkg/interop/runtime"
+)
+
+// Notify1 emits correctly typed event.
+func Notify1() bool {
+	runtime.Notify("Event", interop.Hash160{1, 2, 3})
+
+	return true
+}
+
+// Notify2 emits invalid event (missing from manifest).
+func Notify2() bool {
+	runtime.Notify("AnotherEvent", interop.Hash160{1, 2, 3})
+
+	return true
+}