Replace Iosevka with JetBrains Mono, fix scrollbar and inline edit UX

- Replace embedded Iosevka font with JetBrains Mono as default font
- Fix wide horizontal scrollbar by enabling SCI_SETSCROLLWIDTHTRACKING
- Remove 28-char trailing whitespace padding from all lines
- Fix arrow keys not collapsing selection in inline edit mode
- Dim struct/array braces ({ and };) to match hex node styling
- Resize margin immediately on font change

src/resources.qrc

@@ -4,7 +4,7 @@
         <file alias="chevron-down.png">icons/chevron-down.png</file>
     </qresource>
     <qresource prefix="/fonts">
-        <file alias="Iosevka-Regular.ttf">fonts/Iosevka-Regular.ttf</file>
+        <file alias="JetBrainsMono.ttf">fonts/JetBrainsMono.ttf</file>
     </qresource>
     <qresource prefix="/vsicons">
         <file alias="file.svg">vsicons/file.svg</file>