Update font-related documentation

We now subset Type-1 fonts and no longer have a copy of ttconv.

Make the font comparison table a grid table so we can use a colspan
cell.

Clarify that Type-1 fonts get used only in the usetex/pdf combination.

Author: jkseppan

galleries/users_explain/text/fonts.py

@@ -27,30 +27,35 @@
 Matplotlib supports three font specifications (in addition to pdf 'core fonts',
 which are explained later in the guide):
 
-.. list-table:: Type of Fonts
-   :header-rows: 1
-
-   * - Type 1 (PDF)
-     - Type 3 (PDF/PS)
-     - TrueType (PDF)
-   * - One of the oldest types, introduced by Adobe
-     - Similar to Type 1 in terms of introduction
-     - Newer than previous types, used commonly today, introduced by Apple
-   * - Restricted subset of PostScript, charstrings are in bytecode
-     - Full PostScript language, allows embedding arbitrary code
-       (in theory, even render fractals when rasterizing!)
-     - Include a virtual machine that can execute code!
-   * - These fonts support font hinting
-     - Do not support font hinting
-     - Hinting supported (virtual machine processes the "hints")
-   * - Non-subsetted through Matplotlib
-     - Subsetted via external module ttconv
-     - Subsetted via external module
-       `fontTools <https://github.com/fonttools/fonttools>`__
+.. table:: Type of Fonts
+
+  +--------------------------+----------------------------+----------------------------+
+  | Type 1 (PDF with usetex) | Type 3 (PDF/PS)            | TrueType (PDF)             |
+  +==========================+============================+============================+
+  | One of the oldest types, | Similar to Type 1 in       | Newer than previous types, |
+  | introduced by Adobe      | terms of introduction      | used commonly today,       |
+  |                          |                            | introduced by Apple        |
+  +--------------------------+----------------------------+----------------------------+
+  | Restricted subset of     | Full PostScript language,  | Include a virtual machine  |
+  | PostScript, charstrings  | allows embedding arbitrary | that can execute code!     |
+  | are in bytecode          | code (in theory, even      |                            |
+  |                          | render fractals when       |                            |
+  |                          | rasterizing!)              |                            |
+  +--------------------------+----------------------------+----------------------------+
+  | These fonts support font | Do not support font hinting| Hinting supported (virtual |
+  | hinting                  |                            | machine processes the      |
+  |                          |                            | "hints")                   |
+  +--------------------------+----------------------------+----------------------------+
+  | Subsetted by code in     | Subsetted via external module                           |
+  | `matplotlib._type1font`  | `fontTools <https://github.com/fonttools/fonttools>`__  |
+  +--------------------------+----------------------------+----------------------------+
 
 .. note::
 
    Adobe disabled__ support for authoring with Type 1 fonts in January 2023.
+   Matplotlib uses Type 1 fonts for compatibility with TeX: when the usetex
+   feature is used with the PDF backend, Matplotlib reads the fonts used by
+   the TeX engine, which are usually Type 1.
 
    __ https://helpx.adobe.com/fonts/kb/postscript-type-1-fonts-end-of-support.html
 
@@ -86,11 +91,8 @@
 The solution to this problem is to subset the fonts used in the document and
 only embed the glyphs actually used.  This gets both vector text and small
 files sizes.  Computing the subset of the font required and writing the new
-(reduced) font are both complex problem and thus Matplotlib relies on
-`fontTools <https://fonttools.readthedocs.io/en/latest/>`__ and a vendored fork
-of ttconv.
-
-Currently Type 3, Type 42, and TrueType fonts are subsetted.  Type 1 fonts are not.
+(reduced) font are both complex problems and thus Matplotlib relies in most cases
+on `fontTools <https://fonttools.readthedocs.io/en/latest/>`__.
 
 Core Fonts
 ^^^^^^^^^^