Disable parallel plans for RIGHT_SEMI joins

 Disable parallel plans for RIGHT_SEMI joins
 
 RIGHT_SEMI joins rely on the HEAP_TUPLE_HAS_MATCH flag to guarantee
 that only the first match for each inner tuple is considered.
 However, in a parallel hash join, the inner relation is stored in a
 shared global hash table that can be probed by multiple workers
 concurrently.  This allows different workers to inspect and set the
 match flags of the same inner tuples at the same time.
 
 If two workers probe the same inner tuple concurrently, both may see
 the match flag as unset and emit the same tuple, leading to duplicate
 output rows and violating RIGHT_SEMI join semantics.
 
 For now, we disable parallel plans for RIGHT_SEMI joins.  In the long
 term, it may be possible to support parallel execution by performing
 atomic operations on the match flag, for example using a CAS or
 similar mechanism.
 
 Backpatch to v18, where RIGHT_SEMI join was introduced.
 
 Bug: #19094
 Reported-by: Lori Corbani <Lori.Corbani@jax.org>
 Diagnosed-by: Tom Lane <tgl@sss.pgh.pa.us>
 Author: Richard Guo <guofenglinux@gmail.com>
 Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
 Discussion: https://postgr.es/m/19094-6ed410eb5b256abd@postgresql.org
 Backpatch-through: 18