fix(copy-buttons): resolve issue with copy functionality in developer tools (#2443)

The copy buttons for generated code blocks in Blockly Developer Tools were not functioning correctly in the latest versions of Firefox and Chrome. This fix ensures that the copy buttons work as expected and improves user experience.

Related issue: #2433

Author: jenish-thapa

examples/developer-tools/src/index.html

@@ -149,7 +149,7 @@ <h2>
               <h2>
                 Code Headers
                 <md-icon-button
-                  class="action-button"
+                  class="action-button copy-button"
                   data-owner-id="code-headers"
                   aria-label="Copy code">
                   <md-icon>content_copy</md-icon>
@@ -161,7 +161,7 @@ <h2>
               <h2>
                 Block Definition
                 <md-icon-button
-                  class="action-button"
+                  class="action-button copy-button"
                   data-owner-id="block-definition"
                   aria-label="Copy code">
                   <md-icon>content_copy</md-icon>
@@ -175,7 +175,7 @@ <h2>
               <h2>
                 Generator Stub
                 <md-icon-button
-                  class="action-button"
+                  class="action-button copy-button"
                   data-owner-id="generator-stub"
                   aria-label="Copy code">
                   <md-icon>content_copy</md-icon>