Type/is_supported_index_type: Deal with recursive record types

This plugs the issue reported in #2690, there might be more though.

Closes #2690

testing/btest/Baseline/language.record-recursive-table/output

@@ -0,0 +1,38 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+===, 1, {
+[[bar=1, parent={
+
+}]] = {
+1
+}
+}
+{
+[[bar=1, parent={
+
+}]] = {
+1
+}
+}
+===, 2, {
+[[bar=1, parent={
+
+}]] = {
+1
+},
+[[bar=1, parent={
+[T] = [bar=2, parent={
+
+}]
+}]] = {
+2
+}
+}
+===, 1, {
+[[bar=1, parent={
+[T] = [bar=2, parent={
+
+}]
+}]] = {
+2
+}
+}