Add TimeUnit support.

[jheer]

vega

• Add vega-time utilities.
• Add bar-time test specification.
• Fix dependencies to specific versions. (Why dependencies version are not fixed ? #2089)

vega-encode

• Add support for UTC formatType.
• Update time/utc scale formatting to use vega-time methods.

vega-functions

• Add timeUnitSpecifier expression function.
• Add timeOffset and utcOffset expression functions.
• Add timeSequence and utcSequence expression functions.
• Update timeFormat and utcFormat functions to use vega-time methods.
• Update dependencies.

vega-parser

• Update dependencies.

vega-regression

• Update dependencies.

vega-scale

• Update to use vega-time, drop internal time interval method.

vega-schema

• Add UTC timeFormat to schema.
• Update axis, legend format schema.

vega-statistics

• Update dependencies.

vega-time

• Add new vega-time utility package.

vega-transforms

• Add TimeUnit transform.

vega-typings

• Add TimeUnit transform typings.
• Add UTC timeFormat typing.
• Update axis, legend format typings.

Close #1764.
Close #2084.
Close #2089.

[domoritz]

❤️

[domoritz]

This is awesome.

[anagrius]

Really cool