Request-a-copy: Show correct preview link

[kshepherd]

The preview link was showing an outdated routing path (/access-by-token) instead of the newer, simple item page path with a query parameter.
This small PR fixes that issue and removes some obsolete routing code.

References

• Fixes a small bug in Request-a-copy improvements: Support access by secure link #3984

List of changes in this PR:

• Build item page + query param route in the grant-request-copy component
• Remove outdated access-by-token routing method and path constant

To test, visit the 'grant request' page form with secure links enabled, after requesting an item, and ensure the preview link looks valid (note - it won't work yet as the access hasn't been granted at the time of viewing the form! it's just there for preview / copy paste purposes)

Checklist

• My PR is created against the main branch of code (unless it is a backport or is fixing an issue specific to an older branch).
• My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• My PR passes ESLint validation using npm run lint
• My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• My PR includes details on how to test it. I've provided clear instructions to reviewers on how to successfully test this fix or feature.
• If my PR fixes an issue ticket, I've linked them together.

[tdonohue]

👍 Thanks @kshepherd ! I verified the bug & verified this fixes it.