feat: Support for kerning and ligatures (#873)

## Summary

**What is the goal of this PR?**
Improved typesetting, including
[kerning](https://en.wikipedia.org/wiki/Kerning) and
[ligatures](https://en.wikipedia.org/wiki/Ligature_(writing)#Latin_alphabet).

**What changes are included?**
- The script to convert built-in fonts now adds kerning and ligature
information to the generated font headers.
- Epub page layout calculates proper kerning spaces and makes ligature
substitutions according to the selected font.


![3U1B1808](https://github.com/user-attachments/assets/1accb16f-2f1a-41e5-adca-89f1f1348494)

![3U1B1810](https://github.com/user-attachments/assets/2f6bd007-490e-420f-b774-3380b4add7ea)

![3U1B1815](https://github.com/user-attachments/assets/1986bb77-2db0-46e2-a5d6-8315dae9eb19)

## Additional Context

- I am not a typography expert. 
- The implementation has been reworked from the earlier version, so it
is no longer necessary to omit Open Dyslexic, and kerning data now
covers all fonts, styles, and codepoints for which we include bitmap
data.
- Claude Opus 4.6 helped with a lot of this.
- There's an included test epub document with lots of kerning and
ligature examples, shown in the photos.

**_After some time to mature, I think this change is in decent shape to
merge and get people testing._**

After opening this PR I came across #660, which overlaps in adding
ligature support.

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**YES, Claude Opus 4.6**_

---------

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/GfxRenderer/GfxRenderer.h

@@ -110,6 +110,11 @@ class GfxRenderer {
   void drawText(int fontId, int x, int y, const char* text, bool black = true,
                 EpdFontFamily::Style style = EpdFontFamily::REGULAR) const;
   int getSpaceWidth(int fontId, EpdFontFamily::Style style = EpdFontFamily::REGULAR) const;
+  /// Returns the kerning adjustment for a space between two codepoints:
+  /// kern(leftCp, ' ') + kern(' ', rightCp). Returns 0 if kerning is unavailable.
+  int getSpaceKernAdjust(int fontId, uint32_t leftCp, uint32_t rightCp, EpdFontFamily::Style style) const;
+  /// Returns the kerning adjustment between two adjacent codepoints.
+  int getKerning(int fontId, uint32_t leftCp, uint32_t rightCp, EpdFontFamily::Style style) const;
   int getTextAdvanceX(int fontId, const char* text, EpdFontFamily::Style style) const;
   int getFontAscenderSize(int fontId) const;
   int getLineHeight(int fontId) const;