SearchVM, SearchService: improve search UX by reducing flickering (#1117)

* Fix: don't treat PH OpeningHours with specified time as `everyDay`

* Use SnapshotStateList in SearchVM and don't clear search-results if
there are no new search results from SearchableRepositories

* Rename parameter

* mergeStateLists: refactor as extension method, add apps to SearchResults by default

---------

Co-authored-by: MM20 <15646950+MM2-0@users.noreply.github.com>

services/search/src/main/java/de/mm20/launcher2/search/SearchService.kt

@@ -30,6 +30,7 @@ interface SearchService {
     fun search(
         query: String,
         filters: SearchFilters,
+        initialResults: SearchResults? = null,
     ): Flow<SearchResults>
 
     fun getAllApps(): Flow<AllAppsResults>
@@ -54,9 +55,10 @@ internal class SearchServiceImpl(
     override fun search(
         query: String,
         filters: SearchFilters,
+        initialResults: SearchResults?,
     ): Flow<SearchResults> = flow {
         supervisorScope {
-            val results = MutableStateFlow(SearchResults())
+            val results = MutableStateFlow(initialResults ?: SearchResults())
 
             val customAttrResults = customAttributesRepository.search(query)
                 .map { items ->