Update project page buttons to conform to design system

What does this MR do?

Closes #273286 (closed).

Issues that need fixing upstream

• Star icon svg isn't centered in gitlab-svgs (being fixed in gitlab-svgs#177 (closed))
• Small button dropdown-icon-only doesn't adjust right padding like the md size buttons do
• Small dropdown icon only button's icon need to be 16px

Screenshots (strongly suggested)

Before	After
Info variant	Confirm variant and spacing update

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #273286 (closed)