Rename AnalyzeRequest to AnalyzeTextOptions, and add constructor overloads / helpers for required fields

[heaths]

Per discussion,

• Rename AnalyzeRequest to AnalyzeTextOptions. SearchIndexClient.AnalyzeText should look like: AnalyzeText(string indexName, AnalyzeTextOptions options, ...).
• Add constructor overloads or other initialization helpers to require text, and either analyer or tokenizer (or, if you want, analyzerName, and tokenizerName, though I'll open up a separate issue for that).

class AnalyzeTextOptions {
  ctor(string text, LexicalAnalyzerName analyzer);
  ctor(string text, LexicalTokenizerName tokenizer);
  string text { get; }
  LexicalAnalyzerName? analyzer { get; }
  LexicalTokenizerName? tokenizer { get; }
  (remaining properties: { get; set; })