Expose parseTimeString method and move it to companion object of TimeRangePicker.Time

[pelmenstar1]

This PR changes the implementation of parseTimeString (parsing time is not something complex like parsing e-mail and it can be replaced to simpler implementation). For testing and architectural reasons, it can be exposed and moved to companion object of TimeRangePicker.Time. To ensure that new method works in corrent way, tests was added.

[Droppers]

Thank you a lot again! Looks good and is definitely an improvement!

I am sure there are definitely way more improvements that can be made.

For example, reducing memory allocation:

• getThumbPositions returns a new PointF() instance every time it's called, and it's called a lot
• Matrix() instance created every time gradient is updated, pretty sure that's not necessary.