* Change the IOperation unit test dump format for child nodes

* fixing the newly merged tests.

This PR adds the initial work for a new closure conversion design based around a tree instead of a series of dictionaries. The tree should

Make it easier to assert invariants as we perform rewriting.
Make debugging simpler.
Allow us to move to a series of cheap, simple passes over the simplified tree, rather than one, very complicated pass over the bound tree.
Make it easier to move almost all logic into the analysis phase and make rewriting a simple mechanical transformation.
The heart of the new design is the Scope tree, which consists of a series of nested Scopes, each of which hold relevant information about what variables and closures are declared in that scope. The Closure, meanwhile, holds information for each closure, including a list of captured variables. By carefully visiting the bound node once we should be able to encode all relevant information into the Scope tree, and then iterate over a series of quick, simple passes to create the fully converted form.

Merging on behalf of @tuespetre. Thanks!

Re-using an already-present error message:
MSB3087: An incompatible host object was passed into the "{0}" task.  The host object for this task must implement the "{1}" interface.

changed to return IEnumerable<IOpeartion> from ImmutableArray<IOperation> for IOperationHasChildren and made all IOperation to implement that interface

This allocation was causing 1.4% of all allocations in the trace in https://github.com/dotnet/project-system/issues/2576.

In the new SDK we no longer have a need for ProjectGuid. This change
will:

- Remove ProjectGuid from project files
- Remove Name + Project items from ProjectReference entries
- Change BuildBoss to enforce both of these items

Fixes #20494
Adds a test for #20583

Fixes https://github.com/dotnet/roslyn/issues/19954 and https://github.com/dotnet/roslyn/issues/20125