Add verbose mode for downlevel-dts script

[trivikr]

Is your feature request related to a problem? Please describe.

The downlevel-dts script node scripts/build-downlevel-dts.js does not emit any output while processing declaration types.

Describe the solution you'd like

Use yargs, and except a parameter (say log-level)

• example choices: "silent", "fatal", "error", "warn", "info", "debug", "trace"
• default: "info"

The script should respect the value passed in log-level, and emit logs accordingly.