More layouts: Generators folder, CMake Toolchain, Editable packages and more

[lasote]

Changelog: Feature: Introduced the layout() method to the recipe to be able to declare the folder structure both for the local development methods (conan source, conan build...) and in the cache. Also, associated to the folders, cppinfo objects to be used in editable packages and file pattern descriptions to enable "auto packaging".
Docs: conan-io/docs#2092

• The layout declares a generator folder (defaulted to install_folder if not declared in layout) where the generators and toolchain files are written. The conaninfo and the other weird stuff is kept in the install_folder (probably to be removed in Conan 2.0)
• Also new cppinfo objects in the layout entries.
• The CMake toolchain is injected with an absolute path to the generator folder.
• A little helper for clion layout as an example (not convinced about interface/UX)
• Auto package() based on layout.
• Auto package_info() based on layout.
• Editables following the build and source layouts.

[memsharded]

I have pushed a couple of minor things:

• CMake() was broken for some local flows, because not finding the conanbuild.json file (sorry, no tests, I was checking manually)
• Redundant layout() call, it was already run inside run_configure_method()

Please check ffaa4cb