For @-directives, infer missing semicolon before closing brace (#12792)

For @-directives, infer missing semicolon before closing brace (#12792)

Parser now accepts the following (note missing semicolon after last
@extend-directive):

xyzzy {
  @extend foo ;
  @extend bar
}

As a consequence, moved 31 sasslang-cases from broken to fixed. Moved
two tests from fixed to broken (34, 95, previously passed accidentally)

Change-Id: I8968074abd79dec71be762ed926cc6f37fbcaa99