Consider making Construct stack-aware

[eladb]

We are starting to realize that the fact the Construct is not stack-aware hinders our ability to provide a good experience. For example, to get a handle to the stack, users need to write Stack.find(this) instead of something like this.stack. Similarly, if I want to find a resource, I can use this.findChild but have to cast it down to cdk.Resource. Would have been handy to have this.findResource, etc.

A possible simple solution to this is to convert the base Construct to BaseConstruct and then define a new class Construct which will be Stack and Resource aware and will have the desired APIs.

Brought up by @ccurrie-amzn in a discussion over #784

[rix0rrr]

I would have loved to have something like this before, but I was under the impression the rationale for not having it was to avoid tying ourselves to CloudFormation concepts.

[eladb]

That’s correct, the question is whether we define a Stack as a CloudFormation concept or a more general one.

[rix0rrr]

As an implementation note, StackElement already has a stack property.

[RomainMuller]

I think making stack visible on the .nodes property does not create a strong decision on whether Stack is a CloudFormation or CDK concept. Indeed, it pertains to the top-level Stack class, which we can still have mean anything we'd like, and it could synthesize into a CloudFormation stack AND some not-CloudFormation things.

Anyhow - I'm adding those couple of convenience accessors, because I'm real tired of Stack.find(this).formatArn({ ...});