Allow search URL to support token values

Good job droath! Nice feature.

I found two things:
- The patch was crashing when the block was placed on a page that is not a node. So we need ", required = FALSE" in the contextdefinition
- Why not applying the token replacement on the input name as well, that gives more power to content editors

I will make these adjustments and merge.

This introduced a regression if the "node" module is not enabled. I know it's not very common on Drupal sites but totally possible.

Before the update, it all works, after the update:

The website encountered an unexpected error. Please try again later.

Drupal\Component\Plugin\Exception\PluginNotFoundException: The "entity:node" plugin does not exist. Valid plugin IDs for Drupal\Core\TypedData\TypedDataManager are: filter_format, search_api_html, search_api_text, entity, entity:branch, entity:docblock_class_member, entity:docblock_file, entity:docblock_function, entity:docblock_namespace, entity:docblock_override, entity:docblock_reference, entity:docblock_reference_count, entity:docblock, entity:external_branch, entity:external_documentation, entity:php_branch, entity:php_documentation, entity:project, entity:block, entity:comment, entity:comment:api_comment, entity:comment_type, entity:editor, entity:facets_facet, entity:facets_facet_source, entity:field_config, entity:field_storage_config, entity:file, entity:filter_format, entity:image_style, entity:configurable_language, entity:language_content_settings, entity:menu_link_content, entity:menu_link_content:menu_link_content, entity:path_alias, entity:redirect, entity:redirect:redirect, entity:search_api_index, entity:search_api_server, entity:search_api_task, entity:social_auth, entity:action, entity:menu, entity:user_role, entity:user, entity:pathauto_pattern, entity:view, entity:date_format, entity:entity_form_display, entity:entity_form_mode, entity:entity_view_display, entity:entity_view_mode, entity:base_field_override, entity_reference, field_item:comment, field_item:file, field_item:file_uri, field_item:image, field_item:link, field_item:list_float, field_item:list_integer, field_item:list_string, field_item:path, field_item:redirect_source, field_item:text, field_item:text_long, field_item:text_with_summary, field_item:boolean, field_item:changed, field_item:created, field_item:decimal, field_item:email, field_item:entity_reference, field_item:float, field_item:integer, field_item:language, field_item:map, field_item:password, field_item:string, field_item:string_long, field_item:timestamp, field_item:uri, field_item:uuid, any, binary, boolean, datetime_iso8601, duration_iso8601, email, float, integer, list, language, language_reference, map, string, timespan, timestamp, uri in Drupal\Core\Plugin\DefaultPluginManager->doGetDefinition() (line 53 of core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php).
Drupal\Core\Plugin\DefaultPluginManager->getDefinition('entity:node') (Line: 115)
Drupal\Core\TypedData\TypedDataManager->createDataDefinition('entity:node') (Line: 249)
Drupal\Core\Plugin\Context\ContextDefinition->getDataDefinition() (Line: 123)
Drupal\Core\Plugin\Context\Context->getContextData() (Line: 84)
Drupal\Core\Plugin\Context\Context->hasContextValue() (Line: 125)
Drupal\Core\Plugin\Context\ContextHandler->applyContextMapping(Object, Array) (Line: 122)
Drupal\block\BlockAccessControlHandler->checkAccess(Object, 'view', Object) (Line: 105)

Running a trace, the error is in "SearchBlock.php":

#0 /var/www/html/web/core/lib/Drupal/Component/Plugin/Discovery/DiscoveryCachedTrait.php(25): Drupal\Core\Plugin\DefaultPluginManager->doGetDefinition(Array, 'entity:node', true)
#1 /var/www/html/web/core/lib/Drupal/Core/TypedData/TypedDataManager.php(115): Drupal\Core\Plugin\DefaultPluginManager->getDefinition('entity:node')
#2 /var/www/html/web/core/lib/Drupal/Core/Plugin/Context/ContextDefinition.php(249): Drupal\Core\TypedData\TypedDataManager->createDataDefinition('entity:node')
#3 /var/www/html/web/core/lib/Drupal/Core/Plugin/Context/Context.php(123): Drupal\Core\Plugin\Context\ContextDefinition->getDataDefinition()
#4 /var/www/html/web/core/lib/Drupal/Core/Plugin/Context/Context.php(84): Drupal\Core\Plugin\Context\Context->getContextData()
#5 /var/www/html/web/core/lib/Drupal/Core/Plugin/Context/ContextHandler.php(125): Drupal\Core\Plugin\Context\Context->hasContextValue()
#6 /var/www/html/web/core/modules/block/src/BlockAccessControlHandler.php(122): Drupal\Core\Plugin\Context\ContextHandler->applyContextMapping(Object(Drupal\search_api_block\Plugin\Block\SearchBlock), Array)
#7 /var/www/html/web/core/lib/Drupal/Core/Entity/EntityAccessControlHandler.php(105): Drupal\block\BlockAccessControlHandler->checkAccess(Object(Drupal\block\Entity\Block), 'view', Object(Drupal\Core\Session\AccountProxy))
#8 /var/www/html/web/core/lib/Drupal/Core/Entity/EntityBase.php(314): Drupal\Core\Entity\EntityAccessControlHandler->access(Object(Drupal\block\Entity\Block), 'view', Object(Drupal\Core\Session\AccountProxy), true)
#9 /var/www/html/web/core/modules/block/src/BlockRepository.php(63): Drupal\Core\Entity\EntityBase->access('view', NULL, true)

I'll open a follow up issue with all the above info.