update definition of toDate per cedar-spec#911

[cdisselkoen]

Description of changes

cedar-policy/cedar-spec#911

Issue #, if available

Checklist for requesting a review

The change in this PR is (choose one, and delete the other options):

• A change "invisible" to users (e.g., documentation, changes to "internal" crates like cedar-policy-core, cedar-validator, etc.)

I confirm that this PR (choose one, and delete the other options):

• Updates the "Unreleased" section of the CHANGELOG with a description of my change (required for major/minor version bumps).

I confirm that cedar-spec (choose one, and delete the other options):

• Requires updates, and I have made / will make these updates myself. (Please include in your description a timeline or link to the relevant PR in cedar-spec, and how you have tested that your updates are correct.)

I confirm that docs.cedarpolicy.com (choose one, and delete the other options):

• Does not require updates because my change does not impact the Cedar language specification.

[github-actions]

Coverage Report

Head Commit: a58b7fe9eeb168d7192ad0ecc311f1e9ecb2cf8c

Base Commit: 46405ed696487b337745bb1ed232642932515a65

Download the full coverage report.

Coverage of Added or Modified Lines of Rust Code

Required coverage: 80.00%

Actual coverage: 100.00%

Status: PASSED ✅

Details

File	Status	Covered	Coverage	Missed Lines
cedar-policy-core/src/extensions/datetime.rs	🟢	3/3	100.00%
cedar-policy-symcc/src/symcc/extfun.rs	🟢	5/5	100.00%

Coverage of All Lines of Rust Code

Required coverage: 80.00%

Actual coverage: 86.70%

Status: PASSED ✅

Details

Package	Status	Covered	Coverage	Base Coverage
cedar-language-server	🟢	4722/5102	92.55%	92.55%
cedar-policy	🟡	3754/5096	73.67%	73.67%
cedar-policy-cli	🟡	1120/1565	71.57%	71.57%
cedar-policy-core	🟢	23631/27011	87.49%	87.49%
cedar-policy-formatter	🟢	914/1088	84.01%	84.01%
cedar-policy-symcc	🟢	6740/7260	92.84%	92.84%
cedar-wasm	🔴	0/28	0.00%	0.00%