feat(progress): add parts for more design customization

[brandyscarney]

Features

This adds the following parts to progress bar:

Name	Description
progress	The progress bar that shows the current value (determinate) or slides back and forth (indeterminate).
stream	The animated circles that appear while buffering, only shows when buffer is set and type is "determinate".
track	The track bar is behind the progress bar, if the buffer property is set (determinate) the track will be the width of the buffer value.

Bug fixes

fixes

• setting any of the color variables --progress-background, --background, etc. no longer override the colors set by the color property

resolves #20062 fixes #21820

Demo

Added additional examples to http://localhost:3333/src/components/progress-bar/test/standalone

I modified the progress bar so that you can set the background of the indeterminate using the track part and this also applies to the determinate track / buffer bar, which are the same color. The progress part will apply to the current value in determinate, and the moving bar for indeterminate. The stream part is only relevant for determinate when the buffer value is set.

[liamdebeasi]

The progress animation seems to be broken on both iOS and MD

Screen.Recording.2021-03-03.at.2.44.51.PM.mov

[brandyscarney]

@liamdebeasi Resolved issue with animation

[liamdebeasi]

A few description tweaks, but otherwise this is good to go. Nice job!