fix(material/slider): change color of inactive track

[DBowen33]

trafficstars

change color and remove the opacity of inactive track to pass 3:1 non text color contrast ratio.

https://screenshot.googleplex.com/9xZQAkEaEjY2Ad4

BEFORE: foreground: #E1E3E13d background: #faf9fd ratio: 1.04:1

AFTER: foreground: #74777f background: #faf9fd ratio: 4.27:1

NOTE: This is a significant design change, so curious to see what y'all think of this

fixes b/286300099