Tests: Add a test for LibPDF pattern rendering

This is based largely on Adobe's EXAMPLE 2 on p176 of the specification,
manually edited slightly and then cleaned up with mutool.

https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/PDF32000_2008.pdf

Tests/LibPDF/CMakeLists.txt

@@ -15,6 +15,7 @@ set(TEST_FILES
     non-linearized.pdf
     oss-fuzz-testcase-62065.pdf
     password-is-sup.pdf
+    pattern.pdf
     text.pdf
     type1.pdf
     type3.pdf

Tests/LibPDF/pattern.pdf

@@ -0,0 +1,126 @@
+%PDF-1.7
+%µ¶
+
+1 0 obj
+<</Pages 3 0 R/Type/Catalog>>
+endobj
+
+3 0 obj
+<</Count 1/Kids[5 0 R]/Type/Pages>>
+endobj
+
+5 0 obj
+<</Type/Page/Parent 3 0 R/Resources 10 0 R/Contents 30 0 R/MediaBox[0 0 225 225]>>
+endobj
+
+10 0 obj
+<</Pattern<</P1 15 0 R>>/Font<</F1 20 0 R>>>>
+endobj
+
+15 0 obj
+<</Type/Pattern/PatternType 1/PaintType 1/TilingType 2/BBox[0 0 100 100]/XStep 100/YStep 100/Matrix[.4 0 0 .4 0 0]/Length 632>>
+stream
+BT % Begin text object
+0.0 -0.05 TD % Move text position
+/F1 1 Tf % Set text font and size
+55 0 0 55 7.1771 10.4414 Tm % Set text matrix
+0 Tc % Set character spacing
+0 Tw % Set word spacing
+1.0 0.0 0.0 rg % Set nonstroking colour to red
+( a ) Tj % Show spade glyph
+0.7478 -0.007 TD % Move text position
+0.0 1.0 0.0 rg % Set nonstroking colour to green
+( b ) Tj % Show heart glyph
+-0.7323 0.7813 TD % Move text position
+0.0 0.0 1.0 rg % Set nonstroking colour to blue
+( c ) Tj % Show diamond glyph
+0.6913 0.007 TD % Move text position
+0.0 0.0 0.0 rg % Set nonstroking colour to black
+( d ) Tj % Show club glyph
+ET % End text object
+
+
+endstream
+endobj
+
+20 0 obj
+<</Type/Font/Subtype/Type1/Encoding 21 0 R/BaseFont/Helvevtica>>
+endobj
+
+21 0 obj
+<</Type/Encoding/Differences[1/a109/a110/a111/a112]>>
+endobj
+
+30 0 obj
+<</Length 1086>>
+stream
+0.0 G % Set stroking colour to black
+1.0 1.0 0.0 rg % Set nonstroking colour to yellow
+25 175 175 -150 re % Construct rectangular path
+f % Fill path
+/Pattern cs % Set pattern colour space
+/P1 scn % Set pattern as nonstroking colour
+99.92 49.92 m % Start new path
+99.92 77.52 77.52 99.92 49.92 99.92 c % Construct lower-left circle
+22.32 99.92 -0.08 77.52 -0.08 49.92 c
+-0.08 22.32 22.32 -0.08 49.92 -0.08 c
+77.52 -0.08 99.92 22.32 99.92 49.92 c
+B % Fill and stroke path
+224.96 49.92 m % Start new path
+224.96 77.52 202.56 99.92 174.96 99.92 c % Construct lower-right circle
+147.36 99.92 124.96 77.52 124.96 49.92 c
+124.96 22.32 147.36 -0.08 174.96 -0.08 c
+202.56 -0.08 224.96 22.32 224.96 49.92 c
+B % Fill and stroke path
+87.56 201.70 m % Start new path
+63.66 187.90 55.46 157.32 69.26 133.40 c % Construct upper circle
+83.06 109.50 113.66 101.30 137.56 115.10 c
+161.46 128.90 169.66 159.50 155.86 183.40 c
+142.06 207.30 111.46 215.50 87.56 201.70 c
+B % Fill and stroke path
+50 50 m % Start new path
+175 50 l % Construct triangular path
+112.5 158.253 l
+b % Close, fill, and stroke path 
+endstream
+endobj
+
+xref
+0 31
+0000000002 00001 f 
+0000000016 00000 n 
+0000000004 00003 f 
+0000000062 00000 n 
+0000000006 00003 f 
+0000000114 00000 n 
+0000000007 00003 f 
+0000000008 00003 f 
+0000000009 00003 f 
+0000000011 00003 f 
+0000000213 00000 n 
+0000000012 00003 f 
+0000000013 00003 f 
+0000000014 00003 f 
+0000000016 00003 f 
+0000000276 00000 n 
+0000000017 00003 f 
+0000000018 00003 f 
+0000000019 00003 f 
+0000000022 00003 f 
+0000001071 00000 n 
+0000001153 00000 n 
+0000000023 00003 f 
+0000000024 00003 f 
+0000000025 00003 f 
+0000000026 00003 f 
+0000000027 00003 f 
+0000000028 00003 f 
+0000000029 00003 f 
+0000000000 00003 f 
+0000001224 00000 n 
+
+trailer
+<</Size 31/Root 1 0 R>>
+startxref
+2362
+%%EOF