Bug 1756927 - Fix cert viewer long hex item subpixel scaling. r=sgalich

The expandable overflow fields in the cert viewer have 0px border and 1px
padding by default, and 1px border and 0px padding on hover. Since subpixel
borders are calculated differently from subpixel padding, this causes different
results when window scaling factor is not an integer multiple of 1.

For 1.5x scaling, an input 1px padding can yield either 2px or 1px output
depending on results of scaling algorithm, but an input 1px border will only
yield a 1px output, in order to keep the border crisp and symmetric on every
edge of the bounding box. So when we hover the long hex field, it may lose 1-2
pixels of height as ~1.5px worth of padding (between 1px and 2px) is replaced
with exactly 1px of border.

Patch will fix this by just replacing the 1px padding with a 1px transparent
border. That way the field's height is a function of the same scaling scheme in
all states, so won't change on hover.

Differential Revision: https://phabricator.services.mozilla.com/D139563

toolkit/components/certviewer/content/components/info-item.css

@@ -31,11 +31,15 @@ label {
   margin: 0 5px;
 }
 
+.long-hex {
+  padding: 0;
+  border-block: 1px solid transparent;
+}
+
 .long-hex:hover {
-  border-block: 1px solid var(--in-content-border-color);
+  border-block-color: var(--in-content-border-color);
   background-color: var(--in-content-item-hover);
   color: var(--in-content-item-hover-text);
-  padding: 0;
 }
 
 .hex-open {