Test support of chars beyond BMP in PDF output

Test that character beyond the Basic Multilingual Plane are supported in PDF
files with Type 42 fonts. The example tests STIX Sans math chars and a char
from an old script.

Author: sauerburger

lib/matplotlib/tests/baseline_images/test_text/text_pdf_chars_beyond_bmp.pdf

@@ -748,3 +748,11 @@ def test_pdf_font42_kerning():
     plt.rcParams['pdf.fonttype'] = 42
     plt.figure()
     plt.figtext(0.1, 0.5, "ATAVATAVATAVATAVATA", size=30)
+
+
+@image_comparison(['text_pdf_chars_beyond_bmp.pdf'], style='mpl20')
+def test_pdf_chars_beyond_bmp():
+    plt.rcParams['pdf.fonttype'] = 42
+    plt.rcParams['mathtext.fontset'] = 'stixsans'
+    plt.figure()
+    plt.figtext(0.1, 0.5, "Mass $m$ \U00010308", size=30)