Create migration guidance for Sass functions and mixins

[lgriffee]

Functions

• Create migration guidance for filter() function #5008
• Create migration guidance for px() function #5021
• Create migration guidance for em() function #5022
• Create migration guidance for rem() function #5023
• Create migration guidance for color() function #5071
• Create migration guidance for color-multiply() function #5024
• Create migration guidance for z-index() function #5025
• Create migration guidance for border() function #5026
• Create migration guidance for available-names() function #5027
• Create migration guidance for map-extend() function #5028
• Create migration guidance for spacing() function #5029
• Create migration guidance for easing() function #5030
• Create migration guidance for duration() function #5031
• Create migration guidance for border-radius() function #5032
• Create migration guidance for border-width() function #5094
• Create migration guidance for shadow() function #5033
• Create migration guidance for font-family() function #5034
• Create migration guidance for ms-high-contrast-color() function #5035

Mixins

• Create migration guidance for color-icon() mixin #5009
• Create migration guidance for skeleton-shimmer mixin #5037
• Create migration guidance for state() mixin #5038
• Create migration guidance for skeleton-page-header-layout mixin #5039
• Create migration guidance for skeleton-page-secondary-actions-layout mixin #5040
• Create migration guidance for unstyled-link() mixin #5041
• Create migration guidance for unstyled-list() mixin #5042
• Create migration guidance for high-contrast-outline() and high-contrast-border() mixins #5043
• Create migration guidance for when-printing, when-not-printing, hidden-when-printing, and print-hidden mixins #5044
• Create migration guidance for icon-size() mixin #5045