feat(assets): Change default CSS framework to Tailwind

* enhance(view): Add light default styling for Tailwind
* chore(view): Clean up unnecessary selectors and spacing
* feat(acorn): Update Acorn for Laravel 8.x
* chore(acorn): Create default `bootstrap/` project directory for Laravel 8.x
* refactor(acorn): Split the Acorn bootloader between `functions.php` and `bootstrap/app.php` to coincide with Laravel
* refactor(assets): Lighten the out of the box CSS boilerplate
* refactor(assets): Rename `dist/` to `public/` to coincide with Laravel
* refactor(assets): Flatten the `assets/` directory into `resources/` to coincide with Laravel
* refactor(assets): Rename `scripts/` to `js/` to coincide with Laravel
* refactor(assets): Rename `styles/` to `css/` to coincide with Laravel
* feat(deps): Update to Laravel Mix ^6.0
* chore(deps): Change Mix-related package.json `scripts` to the new `mix` binary
* chore(deps): Remove PurgeCSS in favor of Tailwind's built in purge
* chore(deps): Remove deprecated/unnecessary/unused dependencies
* chore(deps): Bump minimum PHP version to 7.3 to coincide with Laravel 8.x

resources/css/app.scss

@@ -0,0 +1,6 @@
+@import 'tailwindcss/base';
+
+@import 'common/global';
+
+@import 'tailwindcss/components';
+@import 'tailwindcss/utilities';

resources/css/common/global.scss

@@ -0,0 +1,7 @@
+body {
+  @apply font-sans;
+}
+
+.brand {
+  @apply text-3xl font-medium text-indigo-500;
+}

resources/css/editor.scss

@@ -0,0 +1,11 @@
+.block-editor-block-list__layout {
+  @apply font-sans;
+}
+
+.wp-block {
+  @apply max-w-screen-md;
+
+  &.editor-post-title__block .editor-post-title__input {
+    @apply font-sans #{!important};
+  }
+}