Show RCE only after typeing ENTER in text block

closes RCX-3017
flag=block_editor

test plan
  - add a text block to the page
  - click on it
  > expect the toolbar, but not the rce
  - type the ENTER key
  > expect the RCE to open
  - enter some text and save
  > expect the text in the block and the block to be selected
  - ENTER
  > expect the rce again

Change-Id: I0548e43ba7330bed0bd1e261f7b3f9665b0e408d
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/370098


Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jacob DeWar <jacob.dewar@instructure.com>
QA-Review: Jacob DeWar <jacob.dewar@instructure.com>
Product-Review: Ed Schiebel <eschiebel@instructure.com>

ui/shared/block-editor/react/components/user/blocks/RCETextBlock/RCETextBlock.tsx

@@ -121,9 +121,10 @@ export const RCETextBlock = ({text, width, height, sizeVariant = 'auto'}: RCETex
   if (enabled) {
     return (
       <div
-        data-placeholder={I18n.t('Click to edit rich text')}
+        data-placeholder={I18n.t('type <Enter> to edit rich text')}
         role="treeitem"
         aria-label={RCETextBlock.craft.displayName}
+        aria-selected={node.events.selected}
         tabIndex={-1}
         ref={el => {
           el && connect(drag(el))
@@ -131,10 +132,6 @@ export const RCETextBlock = ({text, width, height, sizeVariant = 'auto'}: RCETex
         }}
         className={clazz}
         style={styl}
-        onClick={e => {
-          e.preventDefault()
-          setEditable(true)
-        }}
         onKeyDown={handleKey}
       >
         {renderContent()}