Clean up condition plugins to have schema support and to allow them to be optional

Found only minor things:

1. +++ b/core/lib/Drupal/Core/Condition/ConditionPluginBase.php
   @@ -37,7 +37,7 @@ public function buildConfigurationForm(array $form, array &$form_state) {
   -      '#default_value' => isset($this->configuration['negate']) ? $this->configuration['negate'] : FALSE,
   
   +++ b/core/modules/node/src/Plugin/Condition/NodeType.php
   @@ -80,8 +68,18 @@ public function summary() {
   +    if (empty($this->configuration['bundles']) && !$this->configuration['negate']) {
   
   +++ b/core/modules/user/src/Plugin/Condition/UserRole.php
   @@ -81,6 +80,9 @@ public function summary() {
   +    if (empty($this->configuration['roles']) && !$this->configuration['negate']) {
   

   Shouldn't these use isNegated()?

2. +++ b/core/lib/Drupal/Core/Plugin/ContextAwarePluginBase.php
   @@ -50,4 +60,45 @@ public function setContextValue($name, $value) {
   +      elseif ($value instanceof ContainerInterface) {
   

   ContainerIterface seems not to be imported. Does this work because this special case does not occur during tests? Probably not that relevant as it will be removed with dependency serialization.

This looks good I think. Had to check why the type validation is removed, but it's a checkboxes element, form API already ensures that you can't submit anything that's not part of the selection. Also wtf at Language as Lang....

Committed and pushed to 8.x. Thanks!