let ggen generate longer strings

- StrLen is increased to 16384
- ggen will generate strings up to 16384 but the probability decreases
  with the length of the string
1 job for 14-ggen-string-only-generates-string-up-to-80-chars in 40 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #23699
test

00:00:40