feat(scss): Add bootstrap-5-like grids & media queries

This branch is just for "good to have" optional stand-alone sass features.

In this commit, I aimed to make some things more like bootstrap 5 for ease of use. I  changed the grid breakpoints to match that of Bootstrap 5's and added media query mixins that are more logical like in bootstrap 5.

falcon/_dev/css/abstracts/variables/bootstrap/_grid.scss

@@ -1,3 +1,21 @@
+// Made this more like the breakpoints used in Bootstrap 5
+$grid-breakpoints: (
+    xs: 0,
+    sm: 576px,
+    md: 768px,
+    lg: 992px,
+    xl: 1200px,
+    xxl: 1400px,
+);
+
+$container-max-widths: (
+    sm: 540px,
+    md: 720px,
+    lg: 960px,
+    xl: 1140px,
+    xxl: 1320px,
+);
+
 $grid-columns: 12;
 $grid-gutter-width: rem-calc(20px);
 $grid-row-columns: 6;

falcon/_dev/css/theme/custom/_custom.scss

@@ -6,7 +6,9 @@ https://medium.com/@diyorbekjuraev77/be-a-master-at-creating-the-7-1-sass-patter
 ⚠️NOTE: All bootstrap overrides have been configured under themes/falcon/_dev/css/abstracts/variables/bootstrap */
 
 //Abstracts: Things used throughout the site such as utility classes and generic overrides.
-//@import "abstracts/mixins";
+@import "abstracts/mixins";
+//@import "abstracts/base";
+//@import "abstracts/utilities";
 
 // Components: parts of the theme itself that are not associated with a module.
 //@import "components/buttons";

falcon/_dev/css/theme/custom/abstracts/_mixins.scss

@@ -0,0 +1,44 @@
+// Bootstrap 5-style responsive mixins (more intuitive than Bootstrap 4)
+// Learn the difference here https://getbootstrap.com/docs/5.0/migration/#sass
+
+@mixin bs5-media-breakpoint-up($name) {
+    $min: map-get($grid-breakpoints, $name);
+    @if $min and $min > 0 {
+        @media (min-width: $min) {
+            @content;
+        }
+    } @else {
+        @content;
+    }
+}
+
+@mixin bs5-media-breakpoint-down($name) {
+    $max: map-get($grid-breakpoints, $name);
+    @if $max {
+        @media (max-width: calc(#{$max} - 0.02px)) {
+            @content;
+        }
+    } @else {
+        @content;
+    }
+}
+
+@mixin bs5-media-breakpoint-between($lower, $upper) {
+    $min: map-get($grid-breakpoints, $lower);
+    $max: map-get($grid-breakpoints, $upper);
+    @if $min and $max {
+        @media (min-width: $min) and (max-width: calc(#{$max} - 0.02px)) {
+            @content;
+        }
+    }
+}
+
+@mixin bs5-media-breakpoint-only($name) {
+    $breakpoint-names: map-keys($grid-breakpoints);
+    $index: index($breakpoint-names, $name);
+    $next-name: nth($breakpoint-names, $index + 1);
+
+    @include bs5-media-breakpoint-between($name, $next-name) {
+        @content;
+    }
+}