[core] Inconsistent context type(s)

[fogfish]

The CDK context is defined as a pair string -> any

ConstructNode.setContext(key: string, value: any): void
ConstructNode.tryGetContext(key: string): any

However AppProps defines a context as string -> string pair.

export interface AppProps {
  ...
  readonly context?: {
        [key: string]: string;
    };
}

Reproduction Steps

Once an application start to use JSON structs as a context value then it becomes almost impossible to mock an application with the context (everything works with deployment because context is passed via cdk.json):

const app = new cdk.App({ context: { /* do not allow to pass anything then string -> string pairs */  }  })
app.node.setContext() // fails with error message "unable to modify a tree (or something like that)

Here two major question:

1. Is the usage of JSON structs is valid in the context? I believe yes, because of Vpc.fromLookup does it.
2. Should we change the cdk.App to accept string -> any pair so that we can mock the context

Environment

• CLI Version : 1.47.1 (build 8bb7c0d)
• Framework Version:
• Node.js Version: v12.12.0
• OS : Mac
• **Language (Version):**TypeScript (3.8.3)

[eladb]

Let's change to any. @fogfish would you like to submit a PR?