merge gallium docs into main docs

Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5706>

docs/_exts/formatting.py

@@ -0,0 +1,31 @@
+# formatting.py
+# Sphinx extension providing formatting for Gallium-specific data
+# (c) Corbin Simpson 2010
+# Public domain to the extent permitted; contact author for special licensing
+
+import docutils.nodes
+import sphinx.addnodes
+
+def parse_envvar(env, sig, signode):
+    envvar, t, default = sig.split(" ", 2)
+    envvar = envvar.strip().upper()
+    t = " Type: %s" % t.strip(" <>").lower()
+    default = " Default: %s" % default.strip(" ()")
+    signode += sphinx.addnodes.desc_name(envvar, envvar)
+    signode += sphinx.addnodes.desc_type(t, t)
+    signode += sphinx.addnodes.desc_annotation(default, default)
+    return envvar
+
+def parse_opcode(env, sig, signode):
+    opcode, desc = sig.split("-", 1)
+    opcode = opcode.strip().upper()
+    desc = " (%s)" % desc.strip()
+    signode += sphinx.addnodes.desc_name(opcode, opcode)
+    signode += sphinx.addnodes.desc_annotation(desc, desc)
+    return opcode
+
+def setup(app):
+    app.add_object_type("envvar", "envvar", "%s (environment variable)",
+        parse_envvar)
+    app.add_object_type("opcode", "opcode", "%s (TGSI opcode)",
+        parse_opcode)