Parameterize program solving on a FunctionKind

This new flag determines whether we should introduce a new kind to
represent lambda sets, or whether lambdas should be erased. The latter
is not yet implemented.

crates/compiler/test_solve_helpers/src/lib.rs

@@ -79,6 +79,8 @@ pub fn run_load_and_infer<'a>(
             module_src,
             dir.path().to_path_buf(),
             roc_target::TargetInfo::default_x86_64(),
+            // TODO parameterize me!
+            roc_solve::FunctionKind::LambdaSet,
             roc_reporting::report::RenderTarget::Generic,
             RocCacheDir::Disallowed,
             roc_reporting::report::DEFAULT_PALETTE,