Fix page-provider call in nuxeo-document-content for params='{"system_parentId" : document.uid}'

This issue is also described in https://answers.nuxeo.com/general/q/461fd4b8f46a4e7fb965438ed7c209be/Using-page-providers-in-Web-UI where the solution leads to a bug.

Target platform is 8.10 HF 22+, in which the symptoms seem different from 9.10 release.

In 8.10 HF23 WebUI 1.0.2, constructing a document as:

<nuxeo-document-content role="widget" page-size="5" provider="myAERMPP" params='{"system_parentId" : document.uid}'></nuxeo-document-content>

then the request is:

http://localhost:8080/nuxeo/api/v1/query/myAERMPP?0=\{&1='&2=s&3=y&4=s&5=t&6=e&7=m&8=_&9=p&10=a&11=r&12=e&13=n&14=t&15=I&16=d&17='&18=:&19=c&20=5&21=6&22=9&23=f&24=9&25=5&26=0&27=-&28=d&29=a&30=5&31=f&32=-&33=4&34=3&35=b&36=e&37=-&38=9&39=6&40=2&41=1&42=-&43=4&44=a&45=f&46=1&47=2&48=4&49=f&50=f&51=1&52=b&53=3&54=3&55=,&56=\}&currentPageIndex=0&pageSize=5&sortBy=&sortOrder=

where all characters from the params have been split into individual parameters.

In 9.10 with the same nuxeo-document-content element, then the request appears as:

http://localhost:8080/nuxeo/api/v1/search/pp/myAERMPP/execute?currentPageIndex=0&offset=0&pageSize=6&sortBy=&sortOrder=&ecm_parentId=1a446cfb-5ec6-445f-bdc8-20b365160252

where the ecm_parentId has been changed automatically from system_parentId although Studio does not expect so

With this issue, folderish documents are not able to use page providers as input.
The fix is either for the Studio project to expect ecm_parentId as request input or WebUI runtime not to change verbatim parameter in 9.10.

Same for 8.10 release, with in addition the runtime not to split all characters from the parameter into individual request parameters.