Add test on bytecode text

Test data should be a Kotlin source file with zero or more comments e.g. of
the form: '// 1 INVOKEVIRTUAL'. The test then checks that the generated
bytecode for this file contains exactly one occurrence of the string
'INVOKEVIRTUAL'

compiler/testData/codegen/bytecodeText/statements/ifThenElseEmpty.kt

@@ -0,0 +1,7 @@
+fun foo(b: Boolean) {
+    if (b) {
+    } else {
+    }
+}
+
+// 0 GETSTATIC