Trac #33005: Add feature for pdftocairo

feature `pdf2svg` was introduced in #32650 in order to be used in
#20343. But it turns out that `pdftocairo -svg` is more widely used, for
instance it is available on cygwin as opposed to `pdf2svg`, see
https://trac.sagemath.org/ticket/32650#comment:43

URL: https://trac.sagemath.org/33005
Reported by: slabbe
Ticket author(s): Sébastien Labbé
Reviewer(s): Vincent Delecroix

src/sage/features/poppler.py

@@ -0,0 +1,58 @@
+# -*- coding: utf-8 -*-
+r"""
+Check for poppler features
+
+poppler-utils is a collection of tools built on Poppler's library API, to
+manage PDF and extract contents:
+
+ - ``pdfattach`` - add a new embedded file (attachment) to an existing PDF
+ - ``pdfdetach`` - extract embedded documents from a PDF
+ - ``pdffonts`` - lists the fonts used in a PDF
+ - ``pdfimages`` - extract all embedded images at native resolution from a PDF
+ - ``pdfinfo`` - list all information of a PDF
+ - ``pdfseparate`` - extract single pages from a PDF
+ - ``pdftocairo`` - convert single pages from a PDF to vector or bitmap formats using cairo
+ - ``pdftohtml`` - convert PDF to HTML format retaining formatting
+ - ``pdftoppm`` - convert a PDF page to a bitmap
+ - ``pdftops`` - convert PDF to printable PS format
+ - ``pdftotext`` - extract all text from PDF
+ - ``pdfunite`` - merges several PDF
+
+Currently we only check for the presence of ``pdftocairo``.
+"""
+# ****************************************************************************
+#       Copyright (C) 2021 Sebastien Labbe <slabqc@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#                  https://www.gnu.org/licenses/
+# ****************************************************************************
+
+from . import Executable
+
+class pdftocairo(Executable):
+    r"""
+    A :class:`sage.features.Feature` describing the presence of
+    ``pdftocairo``
+
+    EXAMPLES::
+
+        sage: from sage.features.poppler import pdftocairo
+        sage: pdftocairo().is_present()             # optional: pdftocairo
+        FeatureTestResult('pdftocairo', True)
+    """
+    def __init__(self):
+        r"""
+        TESTS::
+
+            sage: from sage.features.poppler import pdftocairo
+            sage: isinstance(pdftocairo(), pdftocairo)
+            True
+        """
+        Executable.__init__(self, "pdftocairo", executable="pdftocairo",
+                            url="https://poppler.freedesktop.org/")
+
+def all_features():
+    return [pdftocairo()]