FIX: ensures successive tags can be renamed (#12818)

Original bug report: https://meta.discourse.org/t/rename-tag-not-working-as-expected/184950

This bug was caused by the use of `oneWay` which can be very dangerous in this case, from the documentation:

> computed.oneWay only provides an aliased get. The set will not mutate the upstream property, rather causes the current property to become the value set. **This causes the downstream property to permanently diverge from the upstream property.**

app/assets/javascripts/discourse/app/controllers/rename-tag.js

@@ -1,27 +1,24 @@
+import { action } from "@ember/object";
 import BufferedContent from "discourse/mixins/buffered-content";
 import Controller from "@ember/controller";
 import ModalFunctionality from "discourse/mixins/modal-functionality";
 import discourseComputed from "discourse-common/utils/decorators";
 import { extractError } from "discourse/lib/ajax-error";
-import { oneWay } from "@ember/object/computed";
 
 export default Controller.extend(ModalFunctionality, BufferedContent, {
-  tagId: oneWay("model.id"),
+  newTag: null,
 
-  @discourseComputed("tagId", "model.id")
-  renameDisabled(inputTagName, currentTagName) {
+  @discourseComputed("newTag", "model.id")
+  renameDisabled(newTag, currentTag) {
     const filterRegexp = new RegExp(this.site.tags_filter_regexp, "g");
-    const newTagName = inputTagName
-      ? inputTagName.replace(filterRegexp, "").trim()
-      : "";
-
-    return newTagName.length === 0 || newTagName === currentTagName;
+    newTag = newTag ? newTag.replace(filterRegexp, "").trim() : "";
+    return newTag.length === 0 || newTag === currentTag;
   },
 
-  actions: {
+  @action
   performRename() {
     this.model
-        .update({ id: this.get("tagId") })
+      .update({ id: this.newTag })
       .then((result) => {
         this.send("closeModal");
 
@@ -33,5 +30,4 @@ export default Controller.extend(ModalFunctionality, BufferedContent, {
       })
       .catch((error) => this.flash(extractError(error), "error"));
   },
-  },
 });

app/assets/javascripts/discourse/app/templates/modal/rename-tag.hbs

@@ -3,13 +3,19 @@
     {{i18n "tagging.rename_instructions"}}
   </label>
   <div class="controls">
-    {{input value=tagId maxlength=siteSettings.max_tag_length}}
+    {{input
+      value=(readonly model.id)
+      maxlength=siteSettings.max_tag_length
+      input=(action (mut newTag) value="target.value")
+    }}
   </div>
 {{/d-modal-body}}
 
 <div class="modal-footer">
-  {{d-button class="btn-primary"
+  {{d-button
+    class="btn-primary"
     action=(action "performRename")
     label="tagging.rename_tag"
-             disabled=renameDisabled}}
+    disabled=renameDisabled
+  }}
 </div>