Problem/Motivation
Views currently does not show theme suggestions, due to a bug in core: #2118743: Twig debug output does not display all suggestions when an array of theme hooks is passed to #theme
Mark Carver though pointed out in #2118743-167: Twig debug output does not display all suggestions when an array of theme hooks is passed to #theme that views could also use hook_theme_suggestions
Proposed resolution
Use hook_theme_suggestions() instead of arrayed theme hooks.
Remaining tasks
Postponed till #2511548: Add a "context" array variable to all theme hooks and "#context" array property to all elements to provide optional contextual data is finished.
User interface changes
None
API changes
Deprecates ViewsPluginInterface::themeFunctions and ViewExecutable::buildThemeFunctions and replaces them with equivilent themeSuggestions methods.
Data model changes
None