Fix being unable to react with the keycap number sign emoji (#22231)

#⃣

This bug is caused by the emoji consisting of:
U+23 #
U+FE0F
U+20E3  ⃣

Because it starts with a #, it's interpreted as an anchor link, which is not passed to the API. Therefore, the API sees no emoji to react with and answers correctly with a 404.

app/javascript/mastodon/actions/announcements.js

@@ -102,7 +102,7 @@ export const addReaction = (announcementId, name) => (dispatch, getState) => {
     dispatch(addReactionRequest(announcementId, name, alreadyAdded));
   }
 
-  api(getState).put(`/api/v1/announcements/${announcementId}/reactions/${name}`).then(() => {
+  api(getState).put(`/api/v1/announcements/${announcementId}/reactions/${encodeURIComponent(name)}`).then(() => {
     dispatch(addReactionSuccess(announcementId, name, alreadyAdded));
   }).catch(err => {
     if (!alreadyAdded) {
@@ -136,7 +136,7 @@ export const addReactionFail = (announcementId, name, error) => ({
 export const removeReaction = (announcementId, name) => (dispatch, getState) => {
   dispatch(removeReactionRequest(announcementId, name));
 
-  api(getState).delete(`/api/v1/announcements/${announcementId}/reactions/${name}`).then(() => {
+  api(getState).delete(`/api/v1/announcements/${announcementId}/reactions/${encodeURIComponent(name)}`).then(() => {
     dispatch(removeReactionSuccess(announcementId, name));
   }).catch(err => {
     dispatch(removeReactionFail(announcementId, name, err));