fix: encode + sign in url with %2B (googleapis#2094)

Author: ldetmer

google-http-client/src/main/java/com/google/api/client/util/escape/PercentEscaper.java

@@ -61,7 +61,7 @@ public class PercentEscaper extends UnicodeEscaper {
    * specified in RFC 3986. Note that some of these characters do need to be escaped when used in
    * other parts of the URI.
    */
-  public static final String SAFEPATHCHARS_URLENCODER = "-_.!~*'()@:$&,;=+";
+  public static final String SAFEPATHCHARS_URLENCODER = "-_.!~*'()@:$&,;=";
 
   /**
    * A string of characters that do not need to be encoded when used in URI Templates reserved
@@ -72,7 +72,7 @@ public class PercentEscaper extends UnicodeEscaper {
    * href="https://www.rfc-editor.org/rfc/rfc6570#section-3.2.3">RFC 6570 - section 3.2.3</a>.
    */
   public static final String SAFE_PLUS_RESERVED_CHARS_URLENCODER =
-      SAFEPATHCHARS_URLENCODER + "/?#[]";
+      SAFEPATHCHARS_URLENCODER + "+/?#[]";
 
   /**
    * A string of characters that do not need to be encoded when used in URI user info part, as

google-http-client/src/test/java/com/google/api/client/http/UrlEncodedContentTest.java

@@ -62,7 +62,7 @@ public void testWriteTo() throws IOException {
     subtestWriteTo(
         "multi=a&multi=b&multi=c", ArrayMap.of("multi", new String[] {"a", "b", "c"}), true);
     subtestWriteTo("username=un&password=password123;%7B%7D", params, true);
-    subtestWriteTo("additionkey=add+tion", ArrayMap.of("additionkey", "add+tion"), true);
+    subtestWriteTo("additionkey=add%2Btion", ArrayMap.of("additionkey", "add+tion"), true);
   }
 
   private void subtestWriteTo(String expected, Object data, boolean useEscapeUriPathEncoding)