Handle all supported date value types in date picker

[oscar-escire]

References

• Fixes Dynamic form date picker & parser may use date values unsafely #2956
• Malware-Free PR of fix: handle all supported date value types in date picker (#2956) #5163

Description

Replace unsafe .toString() calls on date model values with a new dateValueToString() utility that properly handles all supported types (string, Date, NgbDateStruct) and throws an informative error for unsupported object types.

Instructions for Reviewers

1. Run npm test -- --include="src/app/utils/date.util.spec.ts" — all 32 tests should pass
2. Run npm test -- --include="src/app/shared/form/builder/ds-dynamic-form-ui/models/date-picker/date-picker.component.spec.ts" — all 17 tests should pass
3. Run npm test -- --include="src/app/shared/form/builder/parsers/date-field-parser.spec.ts" — all 3 tests should pass
4. Verify date picker fields work correctly in submission forms (e.g. Date of Issue)

List of changes in this PR:

• Added dateValueToString() utility function in src/app/utils/date.util.ts that safely converts string | Date | object values to YYYY-MM-DD formatted strings
• Updated date-picker.component.ts to use dateValueToString() instead of .toString(), removing the eslint-disable comment and todo
• Updated date-field-parser.ts to use dateValueToString() instead of .toString(), removing the eslint-disable comment and todo
• Added 5 unit tests for dateValueToString() in date.util.spec.ts (string, Date, NgbDateStruct, arbitrary object, empty object)
• Added 2 test suites in date-picker.component.spec.ts to verify initialization from Date and NgbDateStruct-like objects

Checklist

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[GauravD2t]

Hello @oscar-escire, thanks for your contribution. The datetime picker works perfectly on my end, and all test cases passed.

[nathanmlf]

Hey @oscar-escire! I tested it on my side and it works as expected. Nice job!

[tdonohue]

👍 Thanks @oscar-escire ! This looks good to me. The changes are minor overall, and I verified the date field still works the same as before. Not seeing any newly introduced issues

[dspace-bot]

Backport failed for dspace-9_x, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin dspace-9_x
git worktree add -d .worktree/backport-5345-to-dspace-9_x origin/dspace-9_x
cd .worktree/backport-5345-to-dspace-9_x
git switch --create backport-5345-to-dspace-9_x
git cherry-pick -x 639e647d3b992ef8975418943ca17e2de34c3a09