FIX: Make bindMobileUploadButton explicit for upload mixins (#14220)

When using ComposerUpload and/or ComposerUploadUppy, we were
always calling bindMobileUploadButton. However with more composer-like
interfaces being developed, we need this to be optional, as not
everywhere will have a separate mobile upload button to bind to.

Also makes it so the composer extending the ComposerUpload mixins is
responsible for explicitly unbinding the mobile upload button if
it needs to.

app/assets/javascripts/discourse/app/components/composer-editor.js

@@ -219,6 +219,8 @@ export default Component.extend(ComposerUpload, {
     }
 
     this._bindUploadTarget();
+    this._bindMobileUploadButton();
+
     this.appEvents.trigger("composer:will-open");
   },
 
@@ -607,6 +609,7 @@ export default Component.extend(ComposerUpload, {
 
   @on("willDestroyElement")
   _composerClosed() {
+    this._unbindMobileUploadButton();
     this.appEvents.trigger("composer:will-close");
     next(() => {
       // need to wait a bit for the "slide down" transition of the composer

app/assets/javascripts/discourse/app/mixins/composer-upload-uppy.js

@@ -46,11 +46,6 @@ export default Mixin.create({
 
   @on("willDestroyElement")
   _unbindUploadTarget() {
-    this.mobileUploadButton?.removeEventListener(
-      "click",
-      this.mobileUploadButtonEventListener
-    );
-
     this.fileInputEl?.removeEventListener(
       "change",
       this.fileInputEventListener
@@ -86,7 +81,6 @@ export default Mixin.create({
     this._unbindUploadTarget();
     this._bindFileInputChangeListener();
     this._bindPasteListener();
-    this._bindMobileUploadButton();
 
     this._uppyInstance = new Uppy({
       id: this.uppyId,

app/assets/javascripts/discourse/app/mixins/composer-upload.js

@@ -327,8 +327,6 @@ export default Mixin.create({
         }
       });
     });
-
-    this._bindMobileUploadButton();
   },
 
   _bindMobileUploadButton() {
@@ -345,13 +343,15 @@ export default Mixin.create({
     }
   },
 
-  @on("willDestroyElement")
-  _unbindUploadTarget() {
+  _unbindMobileUploadButton() {
     this.mobileUploadButton?.removeEventListener(
       "click",
       this.mobileUploadButtonEventListener
     );
+  },
 
+  @on("willDestroyElement")
+  _unbindUploadTarget() {
     this._validUploads = 0;
     const $uploadTarget = $(this.element);
     try {