doc: fix Type notation in webstreams

Replace `type` with `Type: {Promise}`. Plus, remove duplicated
verb(`Creates and creates` -> `Creates`) in description.

Author: deokjinkim

doc/api/webstreams.md

@@ -895,8 +895,8 @@ added: v16.5.0
 
 * Returns: {WritableStreamDefaultWriter}
 
-Creates and creates a new writer instance that can be used to write
-data into the `WritableStream`.
+Creates a new writer instance that can be used to write data into
+the `WritableStream`.
 
 #### `writableStream.locked`
 
@@ -995,8 +995,8 @@ The amount of data required to fill the {WritableStream}'s queue.
 added: v16.5.0
 -->
 
-* type: A promise that is fulfilled with `undefined` when the
-  writer is ready to be used.
+* Type: {Promise} Fulfilled with `undefined` when the writer is ready
+  to be used.
 
 #### `writableStreamDefaultWriter.releaseLock()`