fix(a11y): add aria-labels to copy-to-clipboard buttons

The copy-to-clipboard buttons across the UI used empty <button/>
elements with no accessible label, making them invisible to screen
readers. This adds descriptive aria-label attributes to:

- cURL command copy button in curl.jsx
- Code highlight copy button in HighlightCode.jsx
- Request snippet copy button in request-snippets.jsx

Partially addresses #10699

Author: yogeshwaran-c

src/core/components/curl.jsx

@@ -18,7 +18,7 @@ export default class Curl extends React.Component {
       <div className="curl-command">
         <h4>Curl</h4>
         <div className="copy-to-clipboard">
-            <CopyToClipboard text={curl}><button/></CopyToClipboard>
+            <CopyToClipboard text={curl}><button aria-label="Copy cURL command to clipboard"/></CopyToClipboard>
         </div>
         <div>
           <SyntaxHighlighter

src/core/plugins/request-snippets/request-snippets.jsx

@@ -133,7 +133,7 @@ const RequestSnippets = ({ request, requestSnippetsSelectors, getComponent }) =>
           </div>
           <div className="copy-to-clipboard">
             <CopyToClipboard text={snippet}>
-              <button />
+              <button aria-label="Copy code snippet to clipboard" />
             </CopyToClipboard>
           </div>
           <div>

src/core/plugins/syntax-highlighting/components/HighlightCode.jsx

@@ -70,7 +70,7 @@ const HighlightCode = ({
       {canCopy && (
         <div className="copy-to-clipboard">
           <CopyToClipboard text={children}>
-            <button />
+            <button aria-label="Copy to clipboard" />
           </CopyToClipboard>
         </div>
       )}