Add CAM16 based color scheme "Dimidium" (#18563)

Okay, here is a challenge for the default color scheme.

This PR adds the [Dimidium] color scheme.

Refs #17818
Refs #18502

I adjusted colors using CAM16. I prioritized lightness so that all
colors (especially blue) has appropriate contrast with the background.

[Brief information about the Dimidium color scheme](https://github.com/dofuuz/dimidium/blob/main/README.md)

[Detailed explanation on crafting the color scheme with CAM16](https://dofuuz.github.io/color/2024/03/17/dimidium-terminal-color-scheme.html)

[Dimidium]: https://github.com/dofuuz/dimidium

Author: dofuuz

.github/actions/spelling/allow/allow.txt

@@ -16,6 +16,7 @@ dcs
 deselection
 dialytika
 diffing
+Dimidium
 dje
 downsides
 dze

src/cascadia/TerminalSettingsModel/defaults.json

@@ -81,6 +81,29 @@
         //   - "foreground"
         //   - "background"
         //   - "cursorColor"
+        {
+            "name": "Dimidium",
+            "background": "#141414",
+            "foreground": "#BAB7B6",
+            "cursorColor": "#37E57B",
+            "selectionBackground": "#FFFFFF",
+            "black": "#000000",
+            "red": "#CF494C",
+            "green": "#60B442",
+            "yellow": "#DB9C11",
+            "blue": "#0575D8",
+            "purple": "#AF5ED2",
+            "cyan": "#1DB6BB",
+            "white": "#BAB7B6",
+            "brightBlack": "#817E7E",
+            "brightRed": "#FF643B",
+            "brightGreen": "#37E57B",
+            "brightYellow": "#FCCD1A",
+            "brightBlue": "#688DFD",
+            "brightPurple": "#ED6FE9",
+            "brightCyan": "#32E0FB",
+            "brightWhite": "#D3D8D9"
+        },
         {
             "name": "Ottosson",
             "background": "#000000",