give importers the headers module templates need

A template defined in a module interface is instantiated in the importing
unit, where its body's types must be complete. A declaration reaching the
importer only through the interface's global module fragment is not
enough for MSVC: cParser::operator>> uses std::stringstream, and every
unit that parsed a float got an incomplete type.

526 headers across 161 units, derived from what each interface's template
bodies actually name.

rendering/nullrenderer.cppm

@@ -2,6 +2,7 @@
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 module;
+#include <ostream>
 #include <cstddef>
 #include <string>
 #include "glad/glad.h"