42797: sql: fix ALTER INDEX IF EXISTS for non-existing index r=rafiss a=rafiss

Previously, if ALTER INDEX IF EXISTS was used on an
unqualified index name that did not match any index, the database would
return an "index does not exist" error.

Now, the statement succeeds, but does nothing.

Also, test edge cases around ambiguous, non-existing, and/or unqualified
index names, in both alter_index and drop_index logic tests.

Fixes #42399 

Release note (bug fix): ALTER INDEX IF EXISTS no longer fails
when using an unqualified index name that does not match any existing
index. Now it is a no-op.

42831: colexec: fix a bug with top K sort not handling K > 1024 r=yuzefovich a=yuzefovich

Previously, top K sorter when emitting the data would copy always from
the beginning of the stored vectors. This is incorrect behavior when
K is greater than coldata.BatchSize(), and now this has been fixed.

Fixes: #42816.

Release note (bug fix): A bug with incorrect handling of Top K sort by
the vectorized engine when K is greater than 1024 has been fixed.

42835: workload, roachtest: skip TPCH Q4 for vec on r=yuzefovich a=yuzefovich

TPCH query 4 in some cases can hit a memory limit error, so we will skip
it for now (until the disk spilling is put in place).

Release note: None

Co-authored-by: Rafi Shamim <rafi@cockroachlabs.com>
Co-authored-by: Yahor Yuzefovich <yahor@cockroachlabs.com>