fix recursive build requires

[memsharded]

Changelog: Bugfix: Solved bug with build-requires transitive build-requires
Changelog: Bugfix: Fixed workspace crash when no layout was specified
Changelog: Bugfix: Do not generate multiple add_subdirectories() for workspaces build-requires

Docs: omit

Close #4752

@tags: slow

[jgsogo]

This PR also fixes/closes/invalidates #3639, with the logic implemented here you cannot repackage using the same name as the build_requires one, it raises with "ERROR: Loop detected: 'my_conanfile_base/1.0.23@lasote/testing' requires 'my_conanfile_base/1.0@lasote/testing' which is an ancestor too". Same if using requires instead of build_requires.

Previously behavior was different:

• for build_requires both libraries were compiled, even if the build_Requires was already available
• for requires it was entering an infinite loop.

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Also, when this PR gets merged, we should revisit #3759 and #3822 (not sure if those will be open questions now).