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-2/output

@@ -0,0 +1,7 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+===, 0, {
+
+}
+===, 1, {
+[[id=1, foo=<uninitialized>]] = [id=2, foo=[id=1, foo=<uninitialized>]]
+}

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
+}
+}

testing/btest/language/record-recursive-table.zeek

@@ -0,0 +1,56 @@
+# @TEST-EXEC: zeek -b %INPUT >output
+# @TEST-EXEC: btest-diff output
+
+type Foo: record {
+	bar: count;
+};
+
+redef record Foo += {
+	parent: table[bool] of Foo &default=table();
+};
+
+event zeek_init()
+	{
+	local tbl: table[Foo] of set[count];
+	local f = Foo($bar=1);
+	tbl[f] = set(1);
+	print "===", |tbl|, tbl;
+	print tbl;
+
+	local parent_tbl: table[bool] of Foo = [
+		[T] = Foo($bar=2),
+	];
+	f$parent = parent_tbl;
+	tbl[f] = set(2);
+
+	# This now has two entries in the table, because
+	# after setting f$parent, that's a different key.
+	print "===", |tbl|, tbl;
+
+	# Mutate f and use it to delete the first entry again.
+	f$parent = table();
+	delete tbl[f];
+
+	# This will be size 1
+	print "===", |tbl|, tbl;
+	}
+
+#@TEST-START-NEXT
+
+type Foo: record {
+	id: string;
+};
+
+redef record Foo += {
+	foo: Foo &optional;
+};
+
+event zeek_init()
+	{
+	local tbl: table[Foo] of Foo;
+	local f1 = Foo($id="1");
+	local f2 = Foo($id="2", $foo=f1);
+	print "===", |tbl|, tbl;
+	tbl[f1] = f2;
+	print "===", |tbl|, tbl;
+	}