ENH: FontDescriptor dataclass

This patch adds a new FontDescriptor dataclass. Its initial use, for
now, is to act as a dataclass for the font metrics of the 14 Adobe
core fonts. These fonts are usually not embedded in PDF documents,
while PDF readers are expected to carry that information themselves.

Author: PJBrs

pypdf/_font.py

@@ -0,0 +1,23 @@
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)
+class FontDescriptor:
+    """
+    Represents the FontDescriptor dictionary as defined in the PDF specification.
+    This contains both descriptive and metric information.
+    """
+
+    name: str
+    family: str
+    weight: str
+
+    ascent: float
+    descent: float
+    cap_height: float
+    x_height: float
+    italic_angle: float
+    flags: int
+    bbox: tuple[float, float, float, float]
+
+    character_widths: dict[str, int]