ps: Explicitly set language level to 3

We currently use various operators from level 2:

- `<<`
- `>>`
- `colorimage`
- `glyphshow`
- `makepattern`
- `rectfill`
- `selectfont`
- `setpagedevice`
- `setpattern`

and from level 3:

- `ShadingType`
- `shfill`
- Type 42 fonts, possibly

without any conditions or fallback, so we should be explicit about what
we require. This is already part of the xpdf distiller at level 2, but
not ghostscript. Since the distiller is optional though, we shouldn't
rely on that.

Author: QuLogic

lib/matplotlib/backends/backend_ps.py

@@ -914,7 +914,8 @@ def print_figure_impl(fh):
                       f"%%DocumentPaperSizes: {papertype}\n"
                       f"%%Pages: 1\n",
                       end="", file=fh)
-            print(f"{dsc_comments}\n"
+            print(f"%%LanguageLevel: 3\n"
+                  f"{dsc_comments}\n"
                   f"%%Orientation: {orientation.name}\n"
                   f"{get_bbox_header(bbox)[0]}\n"
                   f"%%EndComments\n",
@@ -1024,6 +1025,7 @@ def _print_figure_tex(
             tmppath.write_text(
                 f"""\
 %!PS-Adobe-3.0 EPSF-3.0
+%%LanguageLevel: 3
 {dsc_comments}
 {get_bbox_header(bbox)[0]}
 %%EndComments
@@ -1196,7 +1198,7 @@ def xpdf_distill(tmpfile, eps=False, ptype='letter', bbox=None, rotated=False):
              "-dEPSCrop" if eps else "-sPAPERSIZE#%s" % ptype,
              tmpfile, tmppdf], _log)
         cbook._check_and_log_subprocess(
-            ["pdftops", "-paper", "match", "-level2", tmppdf, tmpps], _log)
+            ["pdftops", "-paper", "match", "-level3", tmppdf, tmpps], _log)
         shutil.move(tmpps, tmpfile)
     if eps:
         pstoeps(tmpfile)