Use IndexedScore to accumulate name, description and readme scores.

[isoos]

• This is part of the split of Reduce the memory allocation during search with mutable IndexedScore. #8225.
• The pre-filtering and the text search IndexedScore is not connected yet, will be done in a follow-up PR.
• For each word match calculation we will create a one separate IndexedScore, sparing the creation and merger of multiple Map instances.
• Merging multiple word matches is also done on IndexedScore, filtered package list is carried over efficiently.