[SR-8658] Implement SE-0226 Package Manager Target Based Dependency Resolution

[neonichu]

Previous ID	SR-8658
Radar	rdar://problem/44105619
Original Reporter	@neonichu
Type	New Feature

Additional Detail from JIRA

Votes	6
Component/s	Package Manager
Labels	New Feature
Assignee	None
Priority	Medium

md5: b2a9b01fe8077a3dd6b48f8e8e7ce7ad

Issue Description:

This tracks implementing the SE-0226 Package Manager Target Based Dependency Resolution proposal.
Proposal is here: https://github.com/apple/swift-evolution/blob/master/proposals/0226-package-manager-target-based-dep-resolution.md
This proposal is for enhancing the package resolution process to resolve the minimal set of dependencies that are used in a package graph.

[aciidb0mb3r]

@swift-ci create

[aciidb0mb3r]

Swift 5.2 has partial implementation of this proposal where SwiftPM is able to skip dependencies that are not exported via any product.