internal/core/runtime: temporary helpers to aid transition

Change-Id: I02d59da2c56ef802f5ee1bcbf51e6c77eb481eb9
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/6509
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/internal/core/runtime/index.go b/internal/core/runtime/index.go
index 11c342c..81cb515 100644
--- a/internal/core/runtime/index.go
+++ b/internal/core/runtime/index.go
@@ -52,6 +52,8 @@
 
 var SharedIndexNew = newSharedIndex()
 
+var SharedRuntimeNew = &Runtime{index: SharedIndexNew}
+
 func newSharedIndex() *Index {
 	i := &Index{
 		labelMap:      map[string]int64{"": 0},
diff --git a/internal/core/runtime/runtime.go b/internal/core/runtime/runtime.go
index 61ae9a1..00a68d1 100644
--- a/internal/core/runtime/runtime.go
+++ b/internal/core/runtime/runtime.go
@@ -34,6 +34,10 @@
 	}
 }
 
+func NewWithIndex(x *Index) *Runtime {
+	return &Runtime{index: x}
+}
+
 func (x *Runtime) IndexToString(i int64) string {
 	return x.index.IndexToString(i)
 }