test: migrate 700_e2e rows to corpus fixtures; retire the carrier

136 rows migrated, 0 already owned, 3 wwstage-failing rows held out.

test/wcc/data/r700_match_call_expr/case.ww

@@ -0,0 +1,14 @@
+//ww:run-exit 3
+// Migrated from 700_e2e row 78.
+package main;
+fn make(n: i64) (i64 | str) = {
+  if (n < 0) { return "neg"; };
+  return n + 1;
+};
+fn main() i32 = {
+  match (make(-1)) {
+    case let v: i64 => return v: i32;
+    case let e: str => return e.len: i32;
+  };
+  return 0;
+};