companion: rename S3 upload functions to clarify which type of upload they do

cc @ifedapoolarewaju

packages/@uppy/companion/src/server/Uploader.js

@@ -236,7 +236,7 @@ class Uploader {
       }
 
       if (protocol === PROTOCOLS.s3Multipart && !this.s3Upload) {
-        return this.uploadS3()
+        return this.uploadS3Multipart()
       }
       // @TODO disabling parallel uploads and downloads for now
       // if (!this.options.endpoint) return
@@ -492,7 +492,7 @@ class Uploader {
   /**
    * Upload the file to S3 while it is still being downloaded.
    */
-  uploadS3 () {
+  uploadS3Multipart () {
     const file = createTailReadStream(this.path, {
       tail: true
     })
@@ -501,13 +501,13 @@ class Uploader {
       file.close()
     })
 
-    return this._uploadS3(file)
+    return this._uploadS3MultipartStream(file)
   }
 
   /**
    * Upload a stream to S3.
    */
-  _uploadS3 (stream) {
+  _uploadS3MultipartStream (stream) {
     if (!this.options.s3) {
       this.emitError(new Error('The S3 client is not configured on this companion instance.'))
       return