themes: Swap ANSI white with ANSI black (#32175)

Here’s how it looks after the fix:
![colors](https://github.com/user-attachments/assets/11c78ad6-da50-4aad-b133-9be5e3844878).
White is white and black is black, as intended.

In some cases, dimmed colors were poorly defined, so I took
`text.dimmed` values.

Note that white is defined exactly as the background color for light
themes. Similarly, black is the exact background color for dark themes.
I didn’t change this, but many themes intentionally make white and black
slightly different from the background color. This prevents issues where
programs assume, say, a dark background and set the foreground to white,
making text invisible. I'm not sure if we want to adjust these themes to
address this; just noting it here.


Closes #29379 

Release Notes:

- Fixed ANSI black and ANSI white colors in built-in themes

assets/themes/one/one.json

@@ -450,9 +450,9 @@
         "terminal.foreground": "#242529ff",
         "terminal.bright_foreground": "#242529ff",
         "terminal.dim_foreground": "#fafafaff",
-        "terminal.ansi.black": "#fafafaff",
-        "terminal.ansi.bright_black": "#aaaaaaff",
-        "terminal.ansi.dim_black": "#242529ff",
+        "terminal.ansi.black": "#242529ff",
+        "terminal.ansi.bright_black": "#242529ff",
+        "terminal.ansi.dim_black": "#97979aff",
         "terminal.ansi.red": "#d36151ff",
         "terminal.ansi.bright_red": "#f0b0a4ff",
         "terminal.ansi.dim_red": "#6f312aff",
@@ -471,9 +471,9 @@
         "terminal.ansi.cyan": "#3a82b7ff",
         "terminal.ansi.bright_cyan": "#a3bedaff",
         "terminal.ansi.dim_cyan": "#254058ff",
-        "terminal.ansi.white": "#242529ff",
-        "terminal.ansi.bright_white": "#242529ff",
-        "terminal.ansi.dim_white": "#97979aff",
+        "terminal.ansi.white": "#fafafaff",
+        "terminal.ansi.bright_white": "#fafafaff",
+        "terminal.ansi.dim_white": "#aaaaaaff",
         "link_text.hover": "#5c78e2ff",
         "version_control.added": "#27a657ff",
         "version_control.modified": "#d3b020ff",