Add telemetry to check whether a notebook is Python vs. other languages such as R

[jmew]

No description provided.

[greazer]

We should log whatever language is specified in metadata. Use a whitelist of languages (to avoid possible PII problems). We can use kernel for fallback.

[IanMatthewHuff]

Info Python Extension: 2020-02-18 09:26:55: Telemetry Event : DATASCIENCE.NOTEBOOK_LANGUAGE Measures: undefined Props: {"language":"python","common.os":"win32","common.platformversion":"10.0.18363","common.extname":"ms-python.python","common.extversion":"2020.3.0-dev","common.vscodemachineid":"someValue.machineId","common.vscodesessionid":"someValue.sessionId","common.vscodeversion":"1.42.1"}

Validated in master