Returns the word combinations for the given text based on the combination size.

@param {string} text The text to retrieve combinations for.
@param {number} combinationSize The size of the combinations to retrieve.
@param {Function} functionWords The function containing the lists of function words.
@returns {WordCombination[]} All word combinations for the given text.
function getWordCombinations( text, combinationSize, functionWords ) {
	const sentences = getSentences( text );

	let words, combination;

	return flatMap( sentences, function( sentence ) {
		sentence = sentence.toLocaleLowerCase();
		sentence = normalizeQuotes( sentence );
		words = getWords( sentence );

		return filter( map( words, function( word, i ) {
			// If there are still enough words in the sentence to slice of.
			if ( i + combinationSize - 1 < words.length ) {
				combination = words.slice( i, i + combinationSize );
				return new WordCombination( combination, 0, functionWords );
			}

			return false;
		} ) );
	} );
}