feat: Updates for Policy Framework (#405)

- Documentation
  - Regorus Engine is intended to be used from a single thread
  - Clone the engine after adding policies and data to use from another thread

- Builtin errors strictness:
  - default to less strict for OPA compatibility
  - Provide API to change strictness

- Expose GetAstAsJson to C#,
  This can allow writing policy validations in C#.

- Use spectre mitigated msvc crt libs (binskim compliance)

- Update dependencies

fixes #404

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

bindings/ffi/src/lib.rs

@@ -111,7 +111,12 @@ pub extern "C" fn regorus_result_drop(r: RegorusResult) {
 ///
 /// See https://docs.rs/regorus/latest/regorus/struct.Engine.html
 pub extern "C" fn regorus_engine_new() -> *mut RegorusEngine {
-    let engine = ::regorus::Engine::new();
+    let mut engine = ::regorus::Engine::new();
+
+    // For more OPA compatibility out of the box, we ask builtins to return undefined
+    // instead of raising errors in certain failure scenarios.
+    engine.set_strict_builtin_errors(false);
+
     Box::into_raw(Box::new(RegorusEngine { engine }))
 }
 
@@ -349,6 +354,21 @@ pub extern "C" fn regorus_engine_get_coverage_report(engine: *mut RegorusEngine)
     }
 }
 
+/// Enable/disable strict builtin errors.
+///
+/// See https://docs.rs/regorus/latest/regorus/struct.Engine.html#method.set_strict_builtin_errors
+/// * `strict`: Whether to raise errors or return undefined on certain scenarios.
+#[no_mangle]
+pub extern "C" fn regorus_engine_set_strict_builtin_errors(
+    engine: *mut RegorusEngine,
+    strict: bool,
+) -> RegorusResult {
+    to_regorus_result(|| -> Result<()> {
+        to_ref(&engine)?.engine.set_strict_builtin_errors(strict);
+        Ok(())
+    }())
+}
+
 /// Get pretty printed coverage report.
 ///
 /// See https://docs.rs/regorus/latest/regorus/coverage/struct.Report.html#method.to_string_pretty