MM-21898 - Part 1: Generate and use an interface instead of *A… (#13840)

* Generate and use an interface instead of *App

vendor/modules.txt

@@ -335,7 +335,7 @@ golang.org/x/text/secure/bidirule
 golang.org/x/text/transform
 golang.org/x/text/unicode/bidi
 golang.org/x/text/unicode/norm
-# golang.org/x/tools v0.0.0-20200128002243-345141a36859
+# golang.org/x/tools v0.0.0-20200207224406-61798d64f025
 golang.org/x/tools/go/analysis
 golang.org/x/tools/go/analysis/passes/inspect
 golang.org/x/tools/go/ast/astutil