PLT-4404/PLT-4578/PLT-4541/PLT-4542 Replaced third party autosizing textarea with a custom one (#4442)

* PLT-4578 Replaced third party autosizing textarea with a custom one

* Fix Textbox.handleHeightChange not being called

* Removed unused CSS

* PLT-4541 Force EditPostModal to resize upon opening

* Removed usage of jquery from AutosizeTextarea

* Reverted changes made for PLT-4580 as they're no longer needed

webapp/sass/components/_modal.scss

@@ -21,7 +21,7 @@
 
         .custom-textarea {
             max-height: 60vh;
-            min-height: 20em;
+            min-height: 8em;
         }
 
         .suggestion-list {

webapp/sass/layout/_post.scss

@@ -22,31 +22,6 @@
     color: #d04444 !important;
 }
 
-.textarea-div {
-    border: 0;
-    color: rgba(0,0,0,0);
-    height: auto;
-    left: 1px;
-    line-height: 20px;
-    min-height: 36px;
-    position: absolute;
-    top: 0px;
-    white-space: pre-wrap;
-    word-break: break-word;
-    word-wrap: normal;
-}
-
-body.ios {
-    .textarea-div {
-        -webkit-overflow-scrolling: auto;
-        padding: 7px 17px 7px 15px;
-    }
-}
-
-.textarea-div::-webkit-scrollbar {
-    display: none;
-}
-
 .textarea-wrapper {
     min-height: 36px;
     position: relative;
@@ -390,7 +365,6 @@ body.ios {
 
         .custom-textarea {
             bottom: 0;
-            line-height: 1.5;
             max-height: 162px !important;
             padding-right: 28px;
             padding-top: 8px;