Bug fixes

• Moved configuration to admin/config/development/performance/quicklink
• Renamed and migrated configuration
• Enabled Intersection Observer polyfill by default.
• Vertical tabs interface
• Issue #3021759 by btully: Option to only load library on certain node types
• Display warning on Quicklink settings form if debug mode is enabled.
• Issue #3022882 by andyg5000, mherchel: Add option to prevent Quicklink prefetching when
  sessions are present.

Base theme

• Issue #3 "Unknown "dd" function"
• Removed outdated documentation.
• Added new variable main_layout_attributes contains empty object Attribute() for main layout modifiers on demand.

Starter theme

Fixed code style and comments.
Fixed hook_help example
Added perform.api.php file with description about hooks and alters.

Fixed issues:
#2904359 by Chi: Wrong permission condition in perfmon_page()
#3008848 by yuraosn: Notice: Undefined variable: severity in function perfmon_requirements()

Changes since 8.x-3.11: