Difference in behaviour between prepared and direct create [primary] index statements

We should standardise the behaviour of the various create and drop index statements: for example

create index a on default(a);
create index a on default(a)

fails with 4300

create primary index on default;
create primary index on default;

fails with 5000. should fail with 4300 (or suitable execution error, see later)

create index a on default(a);
prepare ci from create index a on default(a);
drop index default.a;
execute ci;

fails with 4300 on the prepare.
given that it is a legal sequence of requests, it should succeed, much like the following do:

create primary index on default;
prepare cpi from create primary index on default;
drop primary index on default;
execute cpi;

(no index a exists)
prepare st from drop index default.a;
create index a on default(a);
execute st;

(no primary index exists on default)
prepare dpi from drop primary index on default;
create primary index on default;
execute dpi;

Error 4300 should probably be in the execution error range instead.