Include nested senses inside fetched lexemes

The senses, in JSON from Wikidata, get transformed into instances of Z6006.

Added a new Lexeme for testing, primarily because it contains multiple senses. Also, renamed convertLemmas to convertToMultilingualText.

Note: additional tests of handling sense JSON from Wikidata, such as defective cases, will be added when dereferenceLexemeSense gets written (in another MR).

The 2nd commit only replaces the "wd" and "wf" abbreviations in variable names.

Bug: T377547

Closes T377547