Add support for missing operands, invalid method names and invalid variables to 'tolerant-ast' experimental feature

[eidelmanjonathan]

Description of changes

This change expands the 'tolerant-ast' experimental feature to allow for several more error cases to be parsed into partial AST's. This allows us to succeed even if the policy has errors in it.

This change allows us to support the following new cases which will be helpful in creating a better LSP Autocomplete feature in the future:

1. Missing operands, eg: permit(principal ==, action, resource);
2. Invalid method names, eg: permit ( principal,action,resource) when { ip(principal.ip).i() };
3. Invalid variable, eg: permit ( principal,action,resource) when { pri }

Issue #, if available

Checklist for requesting a review

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

• A breaking change requiring a major version bump to cedar-policy (e.g., changes to the signature of an existing API).
• A backwards-compatible change requiring a minor version bump to cedar-policy (e.g., addition of a new API).
• A bug fix or other functionality change requiring a patch to cedar-policy.
• A change "invisible" to users (e.g., documentation, changes to "internal" crates like cedar-policy-core, cedar-validator, etc.)
• [ x ] A change (breaking or otherwise) that only impacts unreleased or experimental code.

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

• [ x ] Updates the "Unreleased" section of the CHANGELOG with a description of my change (required for major/minor version bumps).
• Does not update the CHANGELOG because my change does not significantly impact released code.

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

• [x ] Does not require updates because my change does not impact the Cedar formal model or DRT infrastructure.
• 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.)
• Requires updates, but I do not plan to make them in the near future. (Make sure that your changes are hidden behind a feature flag to mark them as experimental.)
• I'm not sure how my change impacts cedar-spec. (Post your PR anyways, and we'll discuss in the comments.)

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

• [ x ] Does not require updates because my change does not impact the Cedar language specification.
• 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-docs. PRs should be targeted at a staging-X.Y branch, not main.)
• I'm not sure how my change impacts the documentation. (Post your PR anyways, and we'll discuss in the comments.)

[github-actions]

Coverage Report

Head Commit: 508e70823fa69dda671c42663d411ef5741c4e65

Base Commit: 25f7d950cadcfecddaecc2f3ba5af99a0adde0bf

Download the full coverage report.

Coverage of Added or Modified Lines of Rust Code

Required coverage: 80.00%

Actual coverage: 86.30%

Status: PASSED ✅

Details

File	Status	Covered	Coverage	Missed Lines
cedar-policy-core/src/ast/entity.rs	🟢	141/157	89.81%	42, 117-120, 122, 139-143, 427-431
cedar-policy-core/src/ast/policy.rs	🟡	9/12	75.00%	1606, 1664, 1695
cedar-policy-core/src/entities/json/value.rs	🟢	1/1	100.00%
cedar-policy-core/src/est.rs	🟢	11/11	100.00%
cedar-policy-core/src/est/expr.rs	🔴	0/1	0.00%	1143
cedar-policy-core/src/est/scope_constraints.rs	🔴	0/4	0.00%	428, 471, 845, 876
cedar-policy-core/src/parser/cst_to_ast.rs	🟢	201/244	82.38%	336-339, 467-471, 477-481, 486-490, 496-503, 506, 937-940, 942-944, 951, 959-961, 967, 975, 977-978
cedar-policy-core/src/parser/cst_to_ast/to_ref_or_refs.rs	🟢	6/6	100.00%
cedar-policy-core/src/parser/fmt.rs	🟢	17/19	89.47%	65-66
cedar-policy-core/src/parser/text_to_cst.rs	🟢	109/114	95.61%	96-100
cedar-policy-formatter/src/pprint/doc.rs	🟢	31/32	96.88%	191
cedar-policy-validator/src/json_schema.rs	🟢	3/3	100.00%
cedar-policy-validator/src/rbac.rs	🔴	0/2	0.00%	359-360
cedar-policy/src/api.rs	🔴	0/2	0.00%	2832, 3159
cedar-policy/src/proto/policy.rs	🔴	0/5	0.00%	401-405

Coverage of All Lines of Rust Code

Required coverage: 80.00%

Actual coverage: 87.05%

Status: PASSED ✅

Details

Package	Status	Covered	Coverage	Base Coverage
cedar-policy	🟢	10129/11695	86.61%	86.66%
cedar-policy-cli	🔴	526/912	57.68%	57.68%
cedar-policy-core	🟢	12374/14930	82.88%	82.72%
cedar-policy-formatter	🟢	914/1043	87.63%	87.63%
cedar-policy-validator	🟢	20375/21876	93.14%	93.15%
cedar-testing	🔴	0/426	0.00%	0.00%
cedar-wasm	🔴	0/29	0.00%	0.00%