[UIDS] Give Heading default props per level

[kyleshike]

Description

[Description of the problem / solution, screenshots, explanation of approach, links to docs, etc.]
Currently in TS, the Heading component requires all its props be defined. We should provide some sane defaults, perhaps for levels 1-6

User Stories

• As a [persona], I want [feature/task] so that [benefit/reason].
  As an engineer on Rails Server, I want to use the Heading component and not have to think about size, weight, etc.

Acceptance Criteria

• <Heading level={1}> through <Heading level={6}> should each have default values for size and weight.