Add Current Navigation Application Customizer

- Created a new SPFx Application Customizer for current navigation.
- Implemented core functionality to fetch and render navigation items from a SharePoint term set.
- Added styles for the navigation component using SCSS.
- Included localization support for English and German languages.
- Developed unit tests for core navigation functionalities.
- Configured TypeScript and TSLint settings for the project.
- Added validation scripts for static assets and package configuration.

src/extensions/currentNavigation/CurrentNavigation.module.scss

@@ -0,0 +1,91 @@
+@import '~@microsoft/sp-office-ui-fabric-core/dist/sass/SPFabricCore.scss';
+
+:global {
+  .current-navigation {
+    position: relative;
+    z-index: 299;
+    width: 100%;
+    border-bottom: 1px solid $ms-color-neutralLight;
+    background: $ms-color-white;
+    color: $ms-color-neutralPrimary;
+    font-family: $ms-font-family-fallbacks;
+    font-size: $ms-font-size-s;
+  }
+
+  .current-navigation ul {
+    margin: 0;
+    padding: 0;
+    list-style: none;
+  }
+
+  .current-navigation-root {
+    display: flex;
+    min-height: 40px;
+    padding: 0 16px !important;
+  }
+
+  .current-navigation li {
+    position: relative;
+  }
+
+  .current-navigation a,
+  .current-navigation span {
+    display: flex;
+    align-items: center;
+    min-height: 40px;
+    padding: 0 12px;
+    color: inherit;
+    text-decoration: none;
+    white-space: nowrap;
+  }
+
+  .current-navigation a:hover,
+  .current-navigation a:focus,
+  .current-navigation a.is-current {
+    color: $ms-color-themePrimary;
+    background: $ms-color-neutralLighter;
+  }
+
+  .current-navigation a:focus {
+    outline: 2px solid $ms-color-themePrimary;
+    outline-offset: -2px;
+  }
+
+  .current-navigation-children {
+    position: absolute;
+    top: 100%;
+    left: 0;
+    display: none;
+    min-width: 220px;
+    border: 1px solid $ms-color-neutralLight;
+    background: $ms-color-white;
+    box-shadow: 0 4px 12px rgba(0, 0, 0, .16);
+  }
+
+  .current-navigation-children .current-navigation-children {
+    top: 0;
+    left: 100%;
+  }
+
+  .current-navigation li:hover > .current-navigation-children,
+  .current-navigation li:focus-within > .current-navigation-children {
+    display: block;
+  }
+
+  @media (max-width: 767px) {
+    .current-navigation-root {
+      flex-wrap: wrap;
+      padding: 0 8px !important;
+    }
+
+    .current-navigation-children,
+    .current-navigation-children .current-navigation-children {
+      position: static;
+      display: block;
+      min-width: 0;
+      border: 0;
+      box-shadow: none;
+      padding-left: 16px;
+    }
+  }
+}