IBX-8258: richtext: Html5Input is not washed for duplicate IDs

[vidarl]

Question	Answer
JIRA issue	IBX-8258
Bug/Improvement	yes
New feature	no
Target version	3.3
BC breaks	no
Tests pass	yes
Doc needed	no

XSLT stylesheet doesn't check if ids are unique. I wasn't able to reproduce the problem reported in IBX-8258 with the alloy editor ( IDs are note included in the cut&paste operation when performed on Alloy it seems). It is reproducable on the CKEditor in 4.6 The problem is nevertheless represented in the XSLT stylesheet in 3.3 as well

Note: When merging to 4.6, remember to adopt for changes in XML namespaces in new fixtures

TODO:

• [x] Implement feature / fix a bug.
• [x] Implement tests.
• [x] Fix new code according to Coding Standards ($ composer fix-cs).
• [x] Ask for Code Review.