Test/fix internal dependencies in top level manifest.

[dg0yt]

Fixes microsoft/vcpkg#48892.
Implements microsoft/vcpkg#48892 (comment)

This seems to be the first test that actually covers details of handling the top-level manifest, i.e. the request is installing the given top level manifest, not unrelated ports from the registry.
Edit: The difference is how the "source control file" is passed to create_versioned_install_plan.

The PR now includes the e2e test from #1889 because it helps to understand the construction of the test in dependencies.cpp.

[dg0yt]

This reverts a change from #1331 and is the fix for the livelock: Do not reset default_features to false.

• The toplevel request (ConstraintFrame) could include multiple dependencies pointing to the toplevel manifest's default features.
• resolve_stack() calls require_port_defaults() for each of these dependencies.
• The default_features flag of the solution data node (it->second) is what prevents the creation of multiple new resolve_stack items (ConstraintFrame).

[dg0yt]

This is not a revert but retains the actual fix from #1331: Fixing the initialization of the flag.

There are three places which engage the actual default features:

• For the input to the vcpkg install command, default features are initialy unrolled in commands.install.cpp, subject to command line switch.
• For dependencies requested from the toplevel manifest (name), the value is false. Actual default features can be engaged by require_port_defaults(), subject to explicit dependencies in the resolve_stack items (ConstraintFrame).
• For dependencies requested from other manifests, , the value is true. The actual default features are engaged by require_scfl() called three lines later.

[dg0yt]

Now it should be the right fix, rectifying changes from #1331.

I removed cleanup and optimization from this PR. I would submit these usefull improvements after this PR. In addition, I think that PackageNode must become a struct with properly named members instead of a std::pair with non-tell first and second members.