[MM-9777] Avoids adding custom emojis with the same name as a system emoji (#8461)

* Emoji validation fails if name exists in system emojis

* Use hashmap instead of array to improve performance

* Changed utils/StringInMap to emoji/isSystemEmoji

* Load system emojis from model/emoji.json

* Added emoji.json from webapp

* Load system emojis from emoji_data.go instead of emoji.json

* Run `gofmt -w model/emoji_data.go`

1 files changed, 6 insertions, 1 deletions

diff --git a/model/emoji.go b/model/emoji.go
index 47d170bb3..78a266386 100644
--- a/model/emoji.go
+++ b/model/emoji.go
@@ -23,6 +23,11 @@ type Emoji struct {
 	Name      string `json:"name"`
 }
 
+func inSystemEmoji(emojiName string) bool {
+	_, ok := SystemEmojis[emojiName]
+	return ok
+}
+
 func (emoji *Emoji) IsValid() *AppError {
 	if len(emoji.Id) != 26 {
 		return NewAppError("Emoji.IsValid", "model.emoji.id.app_error", nil, "", http.StatusBadRequest)
@@ -40,7 +45,7 @@ func (emoji *Emoji) IsValid() *AppError {
 		return NewAppError("Emoji.IsValid", "model.emoji.user_id.app_error", nil, "", http.StatusBadRequest)
 	}
 
-	if len(emoji.Name) == 0 || len(emoji.Name) > EMOJI_NAME_MAX_LENGTH || !IsValidAlphaNumHyphenUnderscore(emoji.Name, false) {
+	if len(emoji.Name) == 0 || len(emoji.Name) > EMOJI_NAME_MAX_LENGTH || !IsValidAlphaNumHyphenUnderscore(emoji.Name, false) || inSystemEmoji(emoji.Name) {
 		return NewAppError("Emoji.IsValid", "model.emoji.name.app_error", nil, "", http.StatusBadRequest)
 	}