chore(sdk): refactor connections API

[Chriscbr]

Background: in order for Wing classes to support extending non-Wing classes (#3717), I'm trying to remove the Resource class in the SDK so that all classes generated by our compiler just need to extend the ol' construct.Construct class -- the "base class" of the JSII ecosystem. This is a tricky effort since Resource is used in many places, and it collected a lot of responsibilities over the past year.

This PR takes a first step towards that by removing the connection-related information from the Resource class:

wing/libs/wingsdk/src/std/resource.ts

Lines 222 to 223 in 1c9954e

	/** @internal */
	public readonly _connections: Connection[] = [];

Instead, we now store the information inside the root of the construct tree. It can be accessed through Connections.of(x) where x is any class instance. See connections.ts for the full implementation (its short).

With this refactoring, I took the opportunity to clean up how connections are modeled. Previously, we were storing each connection twice inside tree.json (once next to the connection's source, and a second time next to the connection's target). Now, we just store each connection once, in a flat array inside connections.json. (I wasn't sure if it makes more sense to put it in a separate file - I'm interested in feedback on this). I also removed the implicit field which wasn't used by the SDK or console anywhere.

Checklist

• Title matches Winglang's style guide
• Description explains motivation and solution
• Tests added (always)
• Docs updated (only required for features)
• Added pr/e2e-full label if this feature requires end-to-end testing

By submitting this pull request, I confirm that my contribution is made under the terms of the Wing Cloud Contribution License.

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[monadabot]

Congrats! 🚀 This was released in Wing 0.25.15.

[eladb]

I love this direction. See my comment on the Display PR. I think we should merge std.Display and std.Connections into std.Node. This is all node-level general-purpose metadata.