Move LexemeDescription out of search
It doesn't have much to do with search anyway, and it's not specific
to any search engine or function. Thus it can stay in main repo
and be independent of search plugins.
Bug: T216206
Change-Id: If32b1ea0b38b4c1ea5fd9c70d9805782fb3f31a7
Depends-On: I9bbea3d13460ed44755d77fc61ff23fb906cf71e