Normalize all links. (#24109)

* use a trailing slash when possible
* use https when possible
* remove a few redirected links
* consistently use `https://popper.js.org/`
* fix `iconUrl` in nuget files
* change Jekyll Windows guide to the official one

scss/_reboot.scss

@@ -273,7 +273,7 @@ svg:not(:root) {
 // However, they DO support removing the click delay via `touch-action: manipulation`.
 // See:
 // * https://getbootstrap.com/docs/4.0/content/reboot/#click-delay-optimization-for-touch
-// * http://caniuse.com/#feat=css-touch-action
+// * https://caniuse.com/#feat=css-touch-action
 // * https://patrickhlauke.github.io/touch/tests/results/#suppressing-300ms-delay
 
 a,

scss/mixins/_image.scss

@@ -26,7 +26,7 @@
   // Autoprefixer takes care of adding -webkit-min-device-pixel-ratio and -o-min-device-pixel-ratio,
   // but doesn't convert dppx=>dpi.
   // There's no such thing as unprefixed min-device-pixel-ratio since it's nonstandard.
-  // Compatibility info: http://caniuse.com/#feat=css-media-resolution
+  // Compatibility info: https://caniuse.com/#feat=css-media-resolution
   @media
   only screen and (min-resolution: 192dpi), // IE9-11 don't support dppx
   only screen and (min-resolution: 2dppx) { // Standardized

scss/mixins/_screen-reader.scss

@@ -1,7 +1,7 @@
 // Only display content to screen readers
 //
-// See: http://a11yproject.com/posts/how-to-hide-content
-// See: http://hugogiraudel.com/2016/10/13/css-hide-and-seek/
+// See: http://a11yproject.com/posts/how-to-hide-content/
+// See: https://hugogiraudel.com/2016/10/13/css-hide-and-seek/
 
 @mixin sr-only {
   position: absolute;