Ensure that we only have a single design-time build on open

Today, we have a bunch of components hooking up to JointRuleSource and ProjectBuildRuleSource to kick off design-time builds, typically when they are initialized. These trickle in, resulting in unneeded design-time builds during startup.

We should add a service that makes sure given a "normal" project gathers all the known design-time targets we're going to launch, listen to them and making sure we only have a single design-time build during startup.

Start by tracing the components that hook up to JointRuleSource and ProjectBuildRuleSource during initialization. Map the design-time targets gathered for a normal project and how startup builds are triggered. Done means the known startup targets are coordinated so only one design-time build runs, with coverage for the startup behavior.

Written by the indexing model from the issue text.