Fail to set default value for non-required properties in generated code

[xiangyan99]

E.g. I have tsp like:

model PatternTokenizer extends LexicalTokenizer {
/**

• A regular expression pattern to match token separators. Default is an
• expression that matches one or more non-word characters.
  */
  pattern?: string = "\W+";

/**

• Regular expression flags.
  */
  flags?: RegexFlags;

/**

• The zero-based ordinal of the matching group in the regular expression pattern
• to extract into tokens. Use -1 if you want to use the entire pattern to split
• the input into tokens, irrespective of matching groups. Default is -1.
  */
  group?: int32 = -1;

/**

• A URI fragment specifying the type of tokenizer.
  */
  #suppress "@azure-tools/typespec-azure-core/casing-style" "Maintain compatibility with existing models."
  @odata.type: "#Microsoft.Azure.Search.PatternTokenizer";
  }

I expected in the generated code, we set default values for pattern, flags and group. But it does not.

https://github.com/Azure/azure-rest-api-specs/blob/b7ed8b7ef731ee89b71f4ca699a5280800f969d1/specification/search/Azure.Search/models-service.tsp#L7638