feat: refactor heading to support styles as

Created by: gitstart-sourcegraph

Problem Description

To achieve the first requirements of #34741 (closed), we need to create an internal support for Hx to be styled as Hy, within the wildcard header components.

Description

• Support styleAs property in heading components, this would help to perform rendering h2 with h1 style. Using <H2 as={H1} /> couldn't do it since h2 css class has higher priority than h1

Test plan

• There should be no UI changes + unit test snapshot changes

Ref

https://github.com/sourcegraph/sourcegraph/issues/34741

App preview:

• Web
• Storybook

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