lang/evalglue: Different approach to EvalContext defaults for tests

In other packages we've tried being pragmatic by making the main code
compensate for missing arguments in older tests, so that we don't always
need to update every test across the whole system every time we add a new
feature.

However, that compromise unfortunately tends to lead to non-test code
inadvertently relying on the compensations too, so this is an attempt at
a slightly different compromise where the main code will panic if called
incorrectly but there's an extra helper function for tests to fill in
reasonable "inert" defaults for the fields they leave unpopulated.

Signed-off-by: Martin Atkins <mart@degeneration.co.uk>

internal/lang/eval/bench_many_instances_test.go

@@ -14,6 +14,7 @@ import (
 	"github.com/opentofu/opentofu/internal/configs"
 	"github.com/opentofu/opentofu/internal/configs/configschema"
 	"github.com/opentofu/opentofu/internal/lang/eval"
+	"github.com/opentofu/opentofu/internal/lang/eval/internal/evalglue"
 	"github.com/opentofu/opentofu/internal/providers"
 )
 
@@ -65,7 +66,7 @@ func BenchmarkManyResourceInstances(b *testing.B) {
 	// Since there are two resources, there are 2*instanceCount instances total.
 	const instanceCount = 2500
 	configInst, diags := eval.NewConfigInstance(b.Context(), &eval.ConfigCall{
-		EvalContext: &eval.EvalContext{
+		EvalContext: evalglue.EvalContextForTesting(b, &eval.EvalContext{
 			Modules: eval.ModulesForTesting(map[addrs.ModuleSourceLocal]*configs.Module{
 				addrs.ModuleSourceLocal("."): configs.ModuleFromStringForTesting(b, `
 					# This test has two resources that each have a lot of instances
@@ -112,7 +113,7 @@ func BenchmarkManyResourceInstances(b *testing.B) {
 					},
 				},
 			}),
-		},
+		}),
 		RootModuleSource: addrs.ModuleSourceLocal("."),
 		InputValues: eval.InputValuesForTesting(map[string]cty.Value{
 			"instance_count": cty.NumberIntVal(instanceCount),