LibPDF: Implement most of the spec algorithm for picking TrueType glyphs

Non-CID-keyed fonts in PDFs have 8-bit codepoints which are mapped from
bytes to character names via encoding.

TrueType fonts don't index glyphs by name (Type1 fonts do), so the fix
(codified in the spec) was to make a list of all possible glyph names
and map those to (16-bit) unicode values, and then pass those into the
truetype cmap.

(As a fallback, we're supposed to look at the optional names in the
font's "post" table. That part isn't implemented here yet.)

(Note that this affects the behavior of fallback fonts for TrueType
fonts, but not yet fallback fonts for Type1 fonts, and neither the
behavior of the 14 built-in Type1 fonts (which we implement as
fallback fonts), since the TrueType fallback in Type1Font.cpp does
not use this algorithm yet. This will be fixed in a future patch.)

Userland/Libraries/LibPDF/CMakeLists.txt

@@ -6,6 +6,7 @@ set(SOURCES
     Encoding.cpp
     Encryption.cpp
     Filter.cpp
+    Fonts/AdobeGlyphList.cpp
     Fonts/CFF.cpp
     Fonts/PDFFont.cpp
     Fonts/PS1FontProgram.cpp