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_error_alias_str/case.ww

@@ -0,0 +1,16 @@
+//ww:run-exit 3
+// Migrated from 700_e2e row 71.
+package main;
+type error = str;
+fn read(n: i64) (i64 | error) = {
+  if (n < 0) { return "eof": error; };
+  return n + 1;
+};
+fn main() i32 = {
+  let r: (i64 | error) = read(-1);
+  match (r) {
+    case let v: i64 => return v: i32;
+    case let e: error => return e.len: i32;
+  };
+  return 0;
+};