Fixing various accessbility bugs (#4770)

Fixed:
#4259 
#4744
Half of #4749: For the search bar clear button, that comes from an
external component we have no control over.

apps/pwabuilder/src/script/components/discord-box.ts

@@ -80,7 +80,7 @@ export class DiscordBox extends LitElement {
         <div id="discord-box">
           <img id="logo" src="/assets/images/discord_logo.svg" alt="discord logo"/>
           <p>Want to chat? Join us on <a @click=${() => recordPWABuilderProcessStep("discord_box_link_clicked", AnalyticsBehavior.ProcessCheckpoint)} href="https://aka.ms/pwabuilderdiscord" target="_blank" rel="noopener" aria-label="Click to join us on Discord">Discord</a></p>
-          <button id="close-wrapper" @click=${() => this.close()} aria-label="discord modal close" type="button"><img id="close" src="/assets/images/Close_desk.png" role="presentation"/></button>
+          <button id="close-wrapper" @click=${() => this.close()} aria-label="discord modal close" type="button"><sl-icon id="close" name="x-lg"></sl-icon></button>
         </div>`
         : null}
     `;

apps/pwabuilder/src/script/components/share-card.ts

@@ -54,7 +54,7 @@ export class ShareCard extends LitElement {
         top: 5px;
         right: 5px;
         z-index: 1000;
-        color: #C2C9D1;
+        color: #000000;
       }
       .dialog_header {
         height: 12px !important;

docs/builder/android.md

@@ -29,15 +29,15 @@ The first step is to generate your Android package with PWABuilder:
 4. Click on `Generate Package` in the Android section.
 
 <div class="docs-image">
-    <img src="/assets/builder/android/store_package.jpg" width=550>
+    <img src="/assets/builder/android/store_package.jpg" alt="PWABuilder store pacakge selection page showing options to generate packages for both Windows and Android" width=550>
 </div>
 
 5. Make sure you are on the `Google Play` tab and fill out the required options for your package.
 
 6. Click `Download Package`.
 
 <div class="docs-image">
-    <img src="/assets/builder/android/android-options.png" width=550>
+    <img src="/assets/builder/android/android-options.png" alt="Android packaging options page on PWABuilder.com" width=550>
 </div>
 
 ## Configuration Options