spack.concretize: add type-hints, remove kwargs (#47382)

Also remove find_spec, which was used by the old concretizer.
Currently, it seems to be used only in tests.

lib/spack/docs/conf.py

@@ -214,6 +214,7 @@ def setup(sphinx):
     # Spack classes that intersphinx is unable to resolve
     ("py:class", "spack.version.StandardVersion"),
     ("py:class", "spack.spec.DependencySpec"),
+    ("py:class", "spack.spec.ArchSpec"),
     ("py:class", "spack.spec.InstallStatus"),
     ("py:class", "spack.spec.SpecfileReaderBase"),
     ("py:class", "spack.install_test.Pb"),