Tone down color for invisible characters in One themes (#46247)

Related: https://github.com/zed-industries/zed/issues/5592

Coming from vscode, the first thing I noticed (after the amazing speed
that zed started) was the boldness of the whitespace characters.

This mutes the whitespace "invisible" character color in the one theme
so that they are less aggressive. This more closely (but not perfectly)
aligns with the one theme for vscode. In order to avoid adding a new
color to the theme, I reused the `editor.line_number` value in both
cases which worked well.

# Dark
## original:
<img width="858" height="506" alt="before_dark"
src="https://github.com/user-attachments/assets/fe5f1d11-90a5-4fa1-acf6-0d1a25c137f2"
/>

## editor.line_number `#4e5a5f`
<img width="867" height="466" alt="after_dark"
src="https://github.com/user-attachments/assets/5f95f602-43c6-4a1a-9c7d-74b0ea8cf1c9"
/>

## border.variant (alternative) `#363c46ff`
<img width="818" height="489" alt="dark_border_variant"
src="https://github.com/user-attachments/assets/7d44d2f6-e2a4-437e-99d1-ebdf58aab94c"
/>

# Light
## original
<img width="838" height="488" alt="before_light"
src="https://github.com/user-attachments/assets/61e48ba6-487c-468b-b099-4ab0f9ffbc9b"
/>

## editor.line_number `#b4b4bb`
<img width="868" height="493" alt="after_light"
src="https://github.com/user-attachments/assets/d88b74dc-debe-4105-a217-7ca6c4b6ff20"
/>



# Release Notes:

- Improved: Muted the invisible character color in the one themes.

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

assets/themes/one/one.json

@@ -63,7 +63,7 @@
         "editor.line_number": "#4e5a5f",
         "editor.active_line_number": "#d0d4da",
         "editor.hover_line_number": "#acb0b4",
-        "editor.invisible": "#878a98ff",
+        "editor.invisible": "#4e5a5f",
         "editor.wrap_guide": "#c8ccd40d",
         "editor.active_wrap_guide": "#c8ccd41a",
         "editor.document_highlight.read_background": "#74ade81a",
@@ -467,7 +467,7 @@
         "editor.line_number": "#b4b4bb",
         "editor.active_line_number": "#44454b",
         "editor.hover_line_number": "#61616b",
-        "editor.invisible": "#a3a3a4ff",
+        "editor.invisible": "#b4b4bb",
         "editor.wrap_guide": "#383a410d",
         "editor.active_wrap_guide": "#383a411a",
         "editor.document_highlight.read_background": "#5c78e225",