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_chain_ptrfield_write/case.ww

@@ -0,0 +1,12 @@
+//ww:run-exit 47
+// Migrated from 700_e2e row 109.
+package main;
+type inner = struct { tag: u8, pad: u8, flag: i32 };
+type outer = struct { sym: *inner };
+fn main() i32 = {
+  let i: inner = inner { tag = 0u8, pad = 0u8, flag = 10 };
+  let r: outer = outer { sym = &i };
+  r.sym.flag += 32;
+  r.sym.tag = 5u8;
+  return r.sym.flag + (r.sym.tag: i32);
+};