Support writing progress as JSON

[anmenaga]

PR Summary

Fix #592

0. This adds a new argument to dsc.exe:

  -p, --progress-format <PROGRESS_FORMAT>
          Progress format to use [possible values: default, json]

1. For default progress is displayed in UI only;
   for json - progress messages are also written to STDERR stream in JSON form.
2. Fixed a bug with Searching for adapted resources progress which previously was always showing 0.

The structure of json progress message is following. activity and percent_complete are expected to always have value; the rest of the fields are optional.
Same structure will be expected from resources when they will want to provide progress status to dsc (this support will be implemented soon).

pub struct DscProgressValue {
    pub activity:  String,
    pub status: String,
    pub percent_complete: u16,
    pub seconds_remaining: u64,
}

Dev notes:

1. Added struct DscProgressBar which is wrapping both UI progress bar and json serialization; this structure should be used for progress reporting gong forward.

[SteveL-MSFT]

One thing I just realized, the progress output format should not be tied to the result output format. Instead, you should add a top level --progress-format like how we have --trace-format to specify it.

[anmenaga]

One thing I just realized, the progress output format should not be tied to the result output format. Instead, you should add a top level --progress-format like how we have --trace-format to specify it.

Updated code and PR description as suggested.