test(11.1-07): planted fixtures and unit tests for fence, execution and name-form holes

- eighteen violation plants pin nested src=, Go aliases, unrun examples, build membership and command forms
- unit tests cover fence collection, captions, goLang, go doc -c, commandWord and Sync

internal/docsite/testdata/violations/snippet-build-ignored-test-root/modules/demo/demo_test.go

@@ -0,0 +1,15 @@
+package demo
+
+import "testing"
+
+func TestGreet(t *testing.T) {
+	// docs:start greet
+	g := Greeter{Name: "blog"}
+	got := g.Greet()
+	// docs:end greet
+	if got != "Hello, blog" {
+		t.Fatalf("Greet() = %q", got)
+	}
+}
+
+func ignoredOnly() string { return "x" }

internal/docsite/testdata/violations/snippet-build-ignored-test-root/modules/demo/ignored_test.go

@@ -0,0 +1,7 @@
+//go:build ignore
+
+package demo
+
+import "testing"
+
+func TestIgnored(t *testing.T) { _ = ignoredOnly() }