[exploratory] modules/language-models: semantic highlighting component

[cpoerschke]

done-ish list:

• skeleton SemanticHighlightingComponent class in modules/language-models to avoid core/HighlightingComponent.java having modules/language-models dependency
• created CustomModel.java and custom-model.json providing hard-coded mock embeddings for test use without an external model provider dependency
• skeleton logic to use a language model to compute a score for a Passage
• minimal SemanticHighlightingComponentTest class to illustrate usage

to-do list, non-exhaustive:

• consideration of parameter details e.g. how to request semantic highlighting and the model(s) to use
• how to obtain the vector against which passages are compared e.g. from some new parameter directly or by extraction from the q or hl.q parameter if a knn parser is used or by some other way?
• consideration of Passage extraction e.g. currently it is term based but what if the q was a vector query i.e. no terms
• should the PassageScorer and/or the Comparator<Passage> apply the language model to candidate passages?
• how to properly and efficiently compute vector distances? currently using euclidian distance for illustration only.
• tests
• documentation
• ???