Add hasEnrolledInstrument() again (for 1.1)

[marcoscaceres]

Revert "Remove hasEnrolledInstrument() (#930)"

This reverts commit f697360ed9a34fc6974117a66a6a653bf3f2ecd5.

closes #???

The following tasks have been completed:

• [ ] Confirmed there are no ReSpec errors/warnings.
• [ ] Modified Web platform tests (link)
• [ ] Modified MDN Docs (link)
• [ ] Has undergone security/privacy review (link)

Implementation commitment:

• [ ] Safari (link to issue)
• [ ] Chrome (link to issue)
• [ ] Firefox (link to issue)
• [ ] Edge (public signal)

Optional, impact on Payment Handler spec?

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