[JENKINS-74512] Allow configuration editing when content security policy is enabled (#320)

* Use default width for expression editor

Using only half the width is unhelpful

* [JENKINS-74512] Allow configuration editing when content security policy is enabled

https://issues.jenkins.io/browse/JENKINS-74512 notes that the implied
labels plugin fails to edit label implications when content security
policy is enabled.  The configure page reports that the current user
does not have permission to view the page or the page does not exist.

https://www.jenkins.io/doc/developer/security/csp/#legacy-javascript-checkurl-validation
describes the steps that were needed to allow the plugin to support
content security policy.

Testing done:

* Interactive testing confirmed that modifying the expression with a
  valid value produces no error message and saves as expected and that
  modifying with an invalid expression shows a message.  That is the
  same behavior as the current release

* Automated tests all pass

Author: MarkEWaite

src/main/resources/org/jenkinsci/plugins/impliedlabels/Config/configure.jelly

@@ -43,7 +43,7 @@ THE SOFTWARE.
               <f:entry>
                 <label>${%Labels}<f:textbox value="${impl.atomsString()}" field="atoms" style="width: 30%" autoCompleteDelimChar=" " autoCompleteUrl="${rootURL}/label-implications/autoCompleteLabels"/></label>
                 <st:nbsp/>
-                <labels>${%Expression}<f:textbox value="${impl.expressionString()}" field="expression" style="width: 50%" checkUrl="'${rootURL}/label-implications/checkExpression?expression='+encodeURIComponent(this.value)" autoCompleteUrl="${rootURL}/label-implications/autoCompleteLabels" autoCompleteDelimChar=" "/></labels>
+                <labels>${%Expression}<f:textbox value="${impl.expressionString()}" field="expression" checkUrl="${rootURL}/label-implications/checkExpression" checkDependsOn="expression" autoCompleteUrl="${rootURL}/label-implications/autoCompleteLabels" autoCompleteDelimChar=" "/></labels>
                 <st:nbsp/>
                 <f:repeatableDeleteButton />
               </f:entry>