Use CSS color-scheme instead of invert (go-gitea#21616)

The
[`color-scheme`](https://developer.mozilla.org/en-US/docs/Web/CSS/color-scheme)
property changes the base color of certain form elements like the
datepicker icon in Chrome. Set it and remove the previous invert hack.

Before with invert removed:
<img width="840" alt="Screen Shot 2022-10-27 at 11 42 54"
src="https://user-images.githubusercontent.com/115237/198251927-b742e14e-0c62-492c-b667-ee6c69de4ad8.png">
<img width="238" alt="Screen Shot 2022-10-27 at 12 23 28"
src="https://user-images.githubusercontent.com/115237/198260413-37c1ca85-c2de-4c09-8b37-6aa8a23ab575.png">

After:
<img width="841" alt="Screen Shot 2022-10-27 at 11 43 05"
src="https://user-images.githubusercontent.com/115237/198251934-568fa291-0d18-4cd4-adec-58ae1ad90ab2.png">
<img width="839" alt="Screen Shot 2022-10-27 at 11 44 36"
src="https://user-images.githubusercontent.com/115237/198251936-a435105e-572b-41f6-8262-a53820f1d364.png">
<img width="243" alt="Screen Shot 2022-10-27 at 12 23 42"
src="https://user-images.githubusercontent.com/115237/198260432-5eaffc82-ffb8-4559-b1c2-08a39e8f4427.png">

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

web_src/less/_base.less

@@ -168,6 +168,7 @@
   --color-active-line: #fffbdd;
 
   accent-color: var(--color-accent);
+  color-scheme: light;
 }
 
 :root * {

web_src/less/themes/theme-arc-green.less

@@ -153,10 +153,9 @@
   --color-accent: var(--color-primary-light-1);
   --color-small-accent: var(--color-primary-light-5);
   --color-active-line: #534d1b;
-}
 
-::-webkit-calendar-picker-indicator {
-  filter: invert(.8);
+  accent-color: var(--color-accent);
+  color-scheme: dark;
 }
 
 /* invert emojis that are hard to read otherwise */