fix: make //ts:skipLibCheck flag public

[gzm0]

Likely an oversight: all other flags below are public.

We would like to alias this flag to hide the rules_ts dependency and cannot because of the visibility.

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Changes are visible to end-users: yes

• Searched for relevant documentation and updated as needed: Doc update IMO unnecessary.
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: no

Test plan

• Covered by existing test cases

[aspect-workflows]

Test

All tests were cache hits

136 tests (100.0%) were fully cached saving 10s.

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