Improve issue & code search (#33860)

Each "indexer" should provide the "search modes" they support by
themselves. And we need to remove the "fuzzy" search for code.

modules/indexer/code/search.go

@@ -129,7 +129,6 @@ func searchResult(result *internal.SearchResult, startIndex, endIndex int) (*Res
 }
 
 // PerformSearch perform a search on a repository
-// if isFuzzy is true set the Damerau-Levenshtein distance from 0 to 2
 func PerformSearch(ctx context.Context, opts *SearchOptions) (int, []*Result, []*SearchResultLanguages, error) {
 	if opts == nil || len(opts.Keyword) == 0 {
 		return 0, nil, nil, nil