feat(reader): decode simple fonts for text extraction

CHANGELOG.md

@@ -93,6 +93,13 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
   the form's own `/Matrix` into the graphics state's CTM (§8.10.1 b) before interpreting its
   content, so a caller reading the CTM from inside the form's own content sees the composed value,
   not the invoker's own CTM with the form's matrix left for it to apply separately. (#98)
+- **Simple-font decoding for text extraction.** Type1, MMType1 and TrueType fonts map character
+  codes to glyph names through StandardEncoding, WinAnsiEncoding, MacRomanEncoding, the built-in
+  Symbol and ZapfDingbats encodings and `/Differences`, then to Unicode through the Adobe Glyph
+  List (ISO 32000-2 §9.6.5, §9.10.2, Annex D), with `/Widths` and the standard 14 metrics for
+  widths. Five diagnostic codes 400 to 404 report unreadable fonts, malformed encodings or
+  widths, fonts with no route to Unicode, and unmapped glyphs. Text extraction itself lands in a
+  later change. (#98)
 
 ### Changed
 

NOTICE

@@ -31,9 +31,12 @@ Third-party data bundled in this product
 
 Adobe Glyph List
   Location : src/VellumPdf.Conformance/Resources/AdobeGlyphList.txt
+             src/VellumPdf.Reader/Resources/AdobeGlyphList.txt
+             (the Reader copy is byte-identical to the Conformance one)
   Source   : https://github.com/adobe-type-tools/agl-aglfn (glyphlist.txt)
              Bundled copy extracted from veraPDF 1.30.2 (font/AdobeGlyphList.txt)
   Use      : Embedded resource for §7.21.6-2 glyph-name→Unicode compliance check
+             (Conformance) and the glyph-name Unicode route of §9.10.2 (Reader)
   License  : BSD 3-Clause
 
   Copyright 2002-2019 Adobe (http://www.adobe.com/).
@@ -64,6 +67,70 @@ Adobe Glyph List
   ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   POSSIBILITY OF SUCH DAMAGE.
 
+ZapfDingbats glyph list
+  Location : src/VellumPdf.Reader/Resources/ZapfDingbatsGlyphList.txt
+  Source   : https://github.com/adobe-type-tools/agl-aglfn (zapfdingbats.txt)
+             commit 4036a9ca80a62f64f9de4f7321a9a045ad0ecfd6
+  SHA-256  : f6394e3cb8a447e84a1dad75d4baaf2aa7f45dc104faf369f4720e1a774ef2dc
+             (of the committed file, normalised to LF line endings)
+  Use      : Unicode mapping for a ZapfDingbats-flagged simple font's glyph names
+  License  : BSD 3-Clause, same copyright and terms as the Adobe Glyph List above.
+
+Adobe Core 14 AFM font metrics
+  Location : src/VellumPdf.Reader/Fonts/SymbolFontMetrics.cs
+             (a derived table, generated by eng/generate-symbol-font-metrics.py;
+             the AFM files themselves are not committed to this repository)
+  Source   : Adobe Core 14 AFM files (MustRead.html, Adobe Systems, 1997)
+  Use      : Built-in encodings and advance widths for the Symbol and
+             ZapfDingbats fonts (ISO 32000-2 Annex D.5, D.6) and advance widths
+             for the twelve text fonts of the standard 14 when a font
+             dictionary omits /Widths (§9.6.2.2)
+
+  Symbol.afm:
+  Comment Copyright (c) 1985, 1987, 1989, 1990, 1997 Adobe Systems Incorporated.
+  All rights reserved.
+
+  Helvetica.afm, Helvetica-Bold.afm, Helvetica-Oblique.afm,
+  Helvetica-BoldOblique.afm:
+  Comment Copyright (c) 1985, 1987, 1989, 1990, 1997 Adobe Systems
+  Incorporated.  All Rights Reserved.
+
+  ZapfDingbats.afm:
+  Comment Copyright (c) 1985, 1987, 1988, 1989, 1997 Adobe Systems Incorporated.
+  All Rights Reserved.
+
+  Times-Roman.afm, Times-Bold.afm, Times-Italic.afm, Times-BoldItalic.afm:
+  Comment Copyright (c) 1985, 1987, 1989, 1990, 1993, 1997 Adobe Systems
+  Incorporated.  All Rights Reserved.
+
+  Courier.afm, Courier-Oblique.afm:
+  Comment Copyright (c) 1989, 1990, 1991, 1992, 1993, 1997 Adobe Systems
+  Incorporated.  All Rights Reserved.
+
+  Courier-Bold.afm, Courier-BoldOblique.afm:
+  Comment Copyright (c) 1989, 1990, 1991, 1993, 1997 Adobe Systems
+  Incorporated.  All Rights Reserved.
+
+  Helvetica is a trademark of Linotype-Hell AG and/or its subsidiaries.
+  Times is a trademark of Linotype-Hell AG and/or its subsidiaries.
+  ITC Zapf Dingbats is a registered trademark of International Typeface
+  Corporation.
+
+  This file and the 14 PostScript(R) AFM files it accompanies may be used,
+  copied, and distributed for any purpose and without charge, with or without
+  modification, provided that all copyright notices are retained; that the AFM
+  files are not distributed without this file; that all modifications to this
+  file or any of the AFM files are prominently noted in the modified file(s);
+  and that this paragraph is not modified. Adobe Systems has no responsibility
+  or obligation to support the use of the AFM files.
+
+  That licence conditions redistribution of the AFM files themselves on all
+  copyright notices being retained, and SymbolFontMetrics.cs is a derived
+  table of glyph names, codes and advance widths rather than a copy of those
+  files, so the condition does not reach it. This entry reproduces the
+  notices anyway, because a reader of the generated table has no other way to
+  learn where its numbers came from.
+
 ────────────────────────────────────────────────────────────────────────────────
 Third-party data used to build documentation (not bundled)
 ────────────────────────────────────────────────────────────────────────────────