$jsontool and $escapetool should escape { to increase compatibility with XWiki syntax rendering

The output of $jsontool and $escapetool.javascript is frequently used in HTML macros. To prevent that their output could interfere with the closing of the surrounding HTML macro, both should escape {. This also prevents accidental escaping of such output with HTML escaping that would alter the meaning of the content.

Steps to reproduce:

Put one of the following two wiki syntaxes in a document:

{{velocity}}
{{html clean="false"}}
$jsontool.serialize('{{html}}')
{{/html}}
{{/velocity}}

{{velocity}}
{{html clean="false"}}
$escapetool.javascript('{{html}}')
{{/html}}
{{/velocity}}

Expected result:

The text

{{html}}

or

\u007B\u007Bhtml}}

(using JavaScript/JSON escaping for {) is displayed (in quotes for the json tool).

Actual result:

For the first version

"{{html}}" {{/html}} 

is displayed, the second version produces

{{html}} {{/html}}

This shows that due to the extra opening HTML macro syntax, the parser considers the closing HTML macro syntax as content, leading to the unwanted output. This is in particular a problem when the printed text contains user-controlled strings. Both tools already escape "/" so their output cannot close the HTML macro.