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.

share/spack/templates/misc/graph.dot

@@ -0,0 +1,33 @@
+digraph G {
+  labelloc = "b"
+  rankdir = "TB"
+  ranksep = "1"
+  edge[
+     penwidth=2
+  ]
+  node[
+     fontname=Monaco,
+     penwidth=4,
+     fontsize=24,
+     margin=.4,
+     shape=box,
+     fillcolor=lightblue,
+     style="rounded,filled"
+  ]
+
+{% for node, node_options in nodes %}
+{% if node_options %}
+  "{{ node }}" {{ node_options }}
+{% else %}
+  "{{ node }}"
+{% endif %}
+{% endfor %}
+{% for edge_parent, edge_child, edge_options in edges %}
+{% if edge_options %}
+  "{{ edge_parent }}" -> "{{ edge_child }}" {{ edge_options }}
+{% else %}
+  "{{ edge_parent }}" -> "{{ edge_child }}"
+{% endif %}
+{% endfor %}
+
+}