spack graph: rework to use Jinja templates and builders (#34637)

`spack graph` has been reworked to use:

- Jinja templates
- builder objects to construct the template context when DOT graphs are requested. 

This allowed to add a new colored output for DOT graphs that highlights both
the dependency types and the nodes that are needed at runtime for a given spec.

lib/spack/docs/conf.py

@@ -201,12 +201,14 @@ def setup(sphinx):
     ("py:class", "_frozen_importlib_external.SourceFileLoader"),
     ("py:class", "clingo.Control"),
     ("py:class", "six.moves.urllib.parse.ParseResult"),
+    ("py:class", "TextIO"),
     # Spack classes that are private and we don't want to expose
     ("py:class", "spack.provider_index._IndexBase"),
     ("py:class", "spack.repo._PrependFileLoader"),
     ("py:class", "spack.build_systems._checks.BaseBuilder"),
     # Spack classes that intersphinx is unable to resolve
     ("py:class", "spack.version.VersionBase"),
+    ("py:class", "spack.spec.DependencySpec"),
 ]
 
 # The reST default role (used for this markup: `text`) to use for all documents.