Use logical inset properties for ToggleSwitch knob positioning

Replace the four-value inset shorthand with inset-block and
inset-inline-start, dropping the auto filler for the inline-end edge.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: dylanatsmith

app/components/primer/alpha/toggle_switch.pcss

@@ -158,8 +158,9 @@
 
 .ToggleSwitch-knob {
   position: absolute;
-  /* top / bottom / left clear the track border; right stays auto (width drives it) */
-  inset: var(--toggleSwitch-knob-inset) auto var(--toggleSwitch-knob-inset) var(--toggleSwitch-knob-inset);
+  /* clear the track border on the block edges + inline-start; inline-end stays auto (width drives it) */
+  inset-block: var(--toggleSwitch-knob-inset);
+  inset-inline-start: var(--toggleSwitch-knob-inset);
   z-index: 1;
   width: 50%;
   background-color: var(--controlKnob-bgColor-rest);