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_def_str_len/case.ww

@@ -0,0 +1,5 @@
+//ww:run-exit 11
+// Migrated from 700_e2e row 111.
+package main;
+def MSG: str = "hello world";
+fn main() i32 = { return MSG.len: i32; };