Refactor XML services

[caendesilva]

Refactors RssFeedService.php and SitemapService.php

Contains one breaking API change:

• Renames RssFeedService method getDefaultOutputFilename to outputFilename, as the word default implies it can be changed, but we have no such logic.

[codecov]

Codecov Report

Merging #648 (f3beb8e) into master (32dd3ad) will not change coverage.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##              master      #648   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
+ Complexity      1022      1017    -5     
===========================================
  Files            125       126    +1     
  Lines           2543      2540    -3     
===========================================
- Hits            2543      2540    -3     

Impacted Files	Coverage Δ
...ures/BuildTasks/PostBuildTasks/GenerateRssFeed.php	100.00% <100.00%> (ø)
.../Framework/Features/Metadata/GlobalMetadataBag.php	100.00% <100.00%> (ø)
...ramework/src/Framework/Services/RssFeedService.php	100.00% <100.00%> (ø)
...ramework/src/Framework/Services/SitemapService.php	100.00% <100.00%> (ø)
packages/framework/src/Support/Helpers/XML.php	100.00% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.