Support remote components in Python

[justinvp]

Fixes #5354

[justinvp]

Went with an env variable to temporarily enable this, instead of exposing an actual option on ProgramTestOptions, since this is just a temporary workaround.

Originally, I tried doing this as part of building the tests in the Makefile after:

pulumi/Makefile

Lines 71 to 72 in b4c2a35

	test_build:: $(SUB_PROJECTS:%=%_install)
	cd tests/integration/construct_component/testcomponent && yarn install && yarn link @pulumi/pulumi && yarn run tsc

But our beloved CopyFile utility function that we use to copy the test project dir to a temp dir, doesn't handle copying the symlinks that get created inside the node_modules dir when yarn linking @pulumi/pulumi.

[justinvp]

I regenerated the protobuf files because they were stale after changing the remote field from 21 to 20 per https://github.com/pulumi/pulumi/pull/5280/files/9ff12da5cc6477e8f3b4ed17115b1d9bde1e9c39#r483125014

[justinvp]

Note: These cases are slightly different than the Node test, because our Node.js SDK filters out ComponentResources from dependencies, but Python does not.

pulumi/sdk/nodejs/runtime/resource.ts

Lines 392 to 419 in 2585b86

	async function getAllTransitivelyReferencedCustomResourceURNs(resources: Set<Resource>) {
	// Go through 'resources', but transitively walk through **Component** resources, collecting any
	// of their child resources. This way, a Component acts as an aggregation really of all the
	// reachable custom resources it parents. This walking will transitively walk through other
	// child ComponentResources, but will stop when it hits custom resources. in other words, if we
	// had:
	//
	// Comp1
	// / \
	// Cust1 Comp2
	// / \
	// Cust2 Cust3
	// /
	// Cust4
	//
	// Then the transitively reachable custom resources of Comp1 will be [Cust1, Cust2, Cust3]. It
	// will *not* include `Cust4`.
	// To do this, first we just get the transitively reachable set of resources (not diving
	// into custom resources). In the above picture, if we start with 'Comp1', this will be
	// [Comp1, Cust1, Comp2, Cust2, Cust3]
	const transitivelyReachableResources = await getTransitivelyReferencedChildResourcesOfComponentResources(resources);
	const transitivelyReachableCustomResources = [...transitivelyReachableResources].filter(r => CustomResource.isInstance(r));
	const promises = transitivelyReachableCustomResources.map(r => r.urn.promise());
	const urns = await Promise.all(promises);
	return new Set<string>(urns);
	}

So for Python, we need to include the component resources here.