Collect start/end time for each emitter in compiler

[RodgeFu]

Clear and concise description of the problem

Capturing emitter start/end times which would help to identify emitters that are taking longer than others, since they may need to be optimized.

We don't have these data now. We will need the compiler to collect these data and send it to vscode somehow. Seems another reason to do #6663

Checklist

• Follow our Code of Conduct
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[chunyu3]

We also need to collect the execution result of each emitter in typespec compiler which is need for #6663. as following:
{
"result": "pass",
"error": "***", //when emitter fail
}

We can add one more property in Program

export interface EmitResult {
  emitterName: string;
  startTime: dateTime;
  endTime: dateTime;
  result: "fail"|"success"|"skipped";
  error?: string;
}
export interface Program {
   ......
  emits: EmitResult[];
}

[RodgeFu]

The request is from Mario. @mario-guerra , could you help to check with @allenjzhang and @timotheeguerin about whether we need to collect the start/end time for each emitter in compiler? They have some concerns on collecting them. Thanks.

[RodgeFu]

Reopen this after we have a more clear idea about the scenario needs the telemetries.