Mobile: Merge appointment filterer logic and update timezone window

[Tonksthebear]

Summary

Reduce duplicate code between mobile and appointment service. Increases window when determining appointment validity in order to compensate for timezone differences.

Related issue(s)

department-of-veterans-affairs/va-mobile-app#10320

Testing done

Existing tests cover the changes except one was testing functionality when flipper was off

Screenshots

Note: Optional

What areas of the site does it impact?

(Describe what parts of the site are impacted andifcode touched other areas)

Acceptance criteria

• I fixed|updated|added unit tests and integration tests for each feature (if applicable).
• No error nor warning in the console.
• Events are being sent to the appropriate logging solution
• Documentation has been updated (link to documentation)
• No sensitive information (i.e. PII/credentials/internal URLs/etc.) is captured in logging, hardcoded, or specs
• Feature/bug has a monitor built into Datadog (if applicable)
• If app impacted requires authentication, did you login to a local build and verify all authenticated routes work as expected
• I added a screenshot of the developed feature

Requested Feedback

(OPTIONAL)What should the reviewers know in addition to the above. Is there anything specific you wish the reviewer to assist with. Do you have any concerns with this PR, why?

[Tonksthebear]

@simiadebowale Do you have any concerns with me removing the flipper? For mobile, it was always flipped on so for us it made no difference. Just want to confirm web would be ok with the presentation filterer always being used as well

[simiadebowale]

LGTM