Define telemetry data points

[testforstephen]

In order to better manage the telemetry info, we should form a standard about the telemetry data points.
Below is a draft.

Telemetry Type:

• usage
• error
• info

Telemetry entries:

• UsageData
  We divide the extension features into operation unit, and the usage data is based on operation.

Below is the code structure to wrap the telemetry workflow:

try {
  telemetry.start(opId, opName);
  ...execute the operation
  ...
} catch (ex) {
  telemetry.error(ex);
} finally {
  telemetry.end(opId, opName, ex, duration);
}

Below is the telemetry schema:

{
"name": "vscjava.vscode-java-debug/opStart",
"customDimensions": {
   "opId": "<UUID>",
   "opName": "<opName>",
 }
}

{
 "name": "vscjava.vscode-java-debug/opEnd",
 "customDimensions": {
    "opId": "<UUID>",
    "opName": "<opName>",
    "errorMessage": "<message>", // null if it's a success
    "errorCode": 1, // 0 indicates it's a success
    "stackTrace": <>
  },
 "customMeasurements": {
     "duration": 23 // operationFinishTimestamp - operationStartTimestamp, in milliseconds
  }
}

The typical operation units:
(1) we can take the activate extension as an operation, then the opName is activate.
(2) we can take vscode command from vscode.commands.registerCommand as an operation, then the opName is

• Error

{
  "name": "vscjava.vscode-java-debug/error",
  "customDimensions": {
      "errorMessage": "<message>", // null if it's a success
      "errorCode": 1, // 0 indicates it's a success
      "stackTrace": <>
  }
}

• Info
  per extension, log the corresponding diagnostics info.

[testforstephen]

Reference Eskibear/vscode-extension-telemetry-wrapper#7 for new telemetry schema definition.