[JENKINS-26100] Display buildEnv views of available SCM installations.

src/main/resources/org/jenkinsci/plugins/workflow/steps/scm/GenericSCMStep/help.html → src/main/resources/org/jenkinsci/plugins/workflow/steps/scm/GenericSCMStep/help.jelly

@@ -1,4 +1,6 @@
<div>
<?xml version="1.0" encoding="UTF-8"?>
<?jelly escape-by-default='true'?>
<div xmlns:j="jelly:core" xmlns:st="jelly:stapler">
    <p>
    This is a special step that allows to run checkouts using any configuration
    options offered by any Pipeline-compatible SCM plugin.
@@ -17,6 +19,15 @@

        def commitHash = checkout(scm).GIT_COMMIT
    </pre>
    <p>
        Specific variables advertised by installed plugins:
    </p>
    <!-- Cf.  EnvironmentContributor/EnvVarsHtml/index.groovy -->
    <dl class="env-vars">
      <j:forEach var="d" items="${app.getDescriptor('org.jenkinsci.plugins.workflow.steps.scm.GenericSCMStep').applicableDescriptors}">
          <st:include class="${d.clazz}" page="buildEnv" optional="true"/>
      </j:forEach>
    </dl>
    <p>
    Any other specific step to run checkouts (like <code>svn</code> or <code>git</code>)
    are simplistic options of this step.