Using `exists()` in policy with syntax error produces very obtuse stack trace

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

### AI Policy

- [x] I agree to follow this project's AI Policy, or I agree that AI was not used while creating this issue.

### Versions

main

### Operating system

All

### Current Behavior

Broken syntax inside `exists()` like for example:

`exists(foo.bar == "bar")` as opposed to correct syntax `exists(foo, bar == "bar")` gives an obtuse stack trace that gives no information about whats wrong:

```[error] 082eebac-545b-48b4-bb58-2671c09ef121: Exception raised while resolving query.

** (Ash.Error.Unknown)
Bread Crumbs:
> Exception raised in: Safari.Outcrop.PaleoMap.read
> Exception raised in: Safari.Outcrop.Outcrop.read

Unknown Error

* ** (ArgumentError) `nil` is not a Spark DSL module.

nil.persisted(:data_layer)
(spark 2.2.67) lib/spark/dsl/extension.ex:138: Spark.Dsl.Extension.persisted!/3
(ash 3.5.25) lib/ash/filter/filter.ex:3881: Ash.Filter.do_hydrate_refs/2
(ash 3.5.25) lib/ash/filter/filter.ex:3763: Ash.Filter.do_hydrate_refs/2
(safari 0.1.0) lib/safari/policy/end_user_read_access.ex:2: Safari.Policy.EndUserReadAccess.try_strict_check/3
(ash 3.5.25) lib/ash/policy/policy.ex:183: Ash.Policy.Policy.fetch_or_strict_check_fact/2
(ash 3.5.25) lib/ash/policy/policy.ex:427: Ash.Policy.Policy.handle_constants/2
(ash 3.5.25) lib/ash/policy/policy.ex:390: Ash.Policy.Policy.handle_constants/2
(ash 3.5.25) lib/ash/policy/policy.ex:402: Ash.Policy.Policy.handle_constants/2
(ash 3.5.25) lib/ash/policy/policy.ex:390: Ash.Policy.Policy.handle_constants/2
(ash 3.5.25) lib/ash/policy/policy.ex:29: Ash.Policy.Policy.solve/1
(ash 3.5.25) lib/ash/policy/checker.ex:65: Ash.Policy.Checker.strict_check_scenarios/1
(ash 3.5.25) lib/ash/policy/authorizer/authorizer.ex:1724: Ash.Policy.Authorizer.strict_check_result/2
(ash 3.5.25) lib/ash/policy/authorizer/authorizer.ex:693: Ash.Policy.Authorizer.strict_check/2
(ash 3.5.25) lib/ash/can.ex:600: anonymous fn/5 in Ash.Can.run_check/4
(elixir 1.17.2) lib/enum.ex:4858: Enumerable.List.reduce/3
(elixir 1.17.2) lib/enum.ex:2585: Enum.reduce_while/3
(ash 3.5.25) lib/ash/can.ex:597: Ash.Can.run_check/4
(ash 3.5.25) lib/ash/can.ex:198: Ash.Can.can/4
(ash 3.5.25) lib/ash.ex:1807: Ash.can/3

nil.persisted(:data_layer)
(spark 2.2.67) lib/spark/dsl/extension.ex:138: Spark.Dsl.Extension.persisted!/3
(ash 3.5.25) lib/ash/filter/filter.ex:3881: Ash.Filter.do_hydrate_refs/2
(ash 3.5.25) lib/ash/filter/filter.ex:3763: Ash.Filter.do_hydrate_refs/2
(safari 0.1.0) lib/safari/policy/end_user_read_access.ex:2: Safari.Policy.EndUserReadAccess.try_strict_check/3
(ash 3.5.25) lib/ash/policy/policy.ex:183: Ash.Policy.Policy.fetch_or_strict_check_fact/2
(ash 3.5.25) lib/ash/policy/policy.ex:427: Ash.Policy.Policy.handle_constants/2
(ash 3.5.25) lib/ash/policy/policy.ex:390: Ash.Policy.Policy.handle_constants/2
(ash 3.5.25) lib/ash/policy/policy.ex:402: Ash.Policy.Policy.handle_constants/2
(ash 3.5.25) lib/ash/policy/policy.ex:390: Ash.Policy.Policy.handle_constants/2
(ash 3.5.25) lib/ash/policy/policy.ex:29: Ash.Policy.Policy.solve/1
(ash 3.5.25) lib/ash/policy/checker.ex:65: Ash.Policy.Checker.strict_check_scenarios/1
(ash 3.5.25) lib/ash/policy/authorizer/authorizer.ex:1724: Ash.Policy.Authorizer.strict_check_result/2
(ash 3.5.25) lib/ash/policy/authorizer/authorizer.ex:693: Ash.Policy.Authorizer.strict_check/2
(ash 3.5.25) lib/ash/can.ex:600: anonymous fn/5 in Ash.Can.run_check/4
(elixir 1.17.2) lib/enum.ex:4858: Enumerable.List.reduce/3
(elixir 1.17.2) lib/enum.ex:2585: Enum.reduce_while/3
(ash 3.5.25) lib/ash/can.ex:597: Ash.Can.run_check/4
(ash 3.5.25) lib/ash/can.ex:198: Ash.Can.can/4
(ash 3.5.25) lib/ash.ex:1807: Ash.can/3
```

### Reproduction

Just make an invalid exists.

### Expected Behavior

Invalid exists either gives stack trace with information that the exists is wrongly done or it errors already at compile time.

Reproduce the invalid `exists(foo.bar == "bar")` policy and trace the failure through `lib/ash/filter/filter.ex` at `do_hydrate_refs/2`, then through the policy stack shown in the report. Compare it with the valid two-argument form and inspect existing filter or policy coverage. Done means the invalid form reports the malformed `exists` clearly or fails during compilation instead of producing the shown `nil.persisted(:data_layer)` trace.

Written by the indexing model from the issue text.