page_manager 8.x-1.0-alpha6

Changes since 8.x-1.0-alpha3:

• #2413407 by Berdir: Theme logos are now svg, breaks theme tests
• #2409321 by rlmumford, Berdir: Update Page Manager Tests for new Immutable Config.
• Sacrifice DX for no real gain, and adjust to new requirement that has no reasoning behind it: #2281645.
• #2391925 by tim.plunkett: Temporarily prevent test failures from invalid config schema.
• Begin to fix configuration schema issues.
• Restore @group to certain tests.
• Fix which namespaces are used.
• Remove obsolete copyFormValuesToEntity() implementation.
• Typehint with PageExecutableInterface.
• Remove old wrapper around drupal_html_class().
• Use $this->t() when possible.
• Switch to short array syntax everywhere.
• Update metadata on test classes.
• Install stark, thanks to #2350823
• Use the correct ContextAwarePluginInterface in BlockDisplayVariantTest.
• Stop using the deprecated _content in routing.
• Update for #2339151 in core.