MySQLnd: Support cursors in store/get result

This fixes two related issues:

1. When a PS with cursor is used in store_result/get_result,
perform a COM_FETCH with maximum numb

MySQLnd: Support cursors in store/get result

This fixes two related issues:

1. When a PS with cursor is used in store_result/get_result,
perform a COM_FETCH with maximum number of rows rather than
silently switching to an unbuffered result set (in the case of
store_result) or erroring (in the case of get_result).
In the future, we might want to make get_result unbuffered for
PS with cursors, as using cursors with buffered result sets
doesn't really make sense. Unlike store_result, get_result
isn't very explicit about what kind of result set is desired.
2. If the client did not request a cursor, but the server reports
that a cursor exists, ignore this and treat the PS as if it
has no cursor (i.e. to not use COM_FETCH). It appears to be a
server side bug that a cursor used inside an SP will be reported
to the client, even though the client cannot use the cursor.

Fixes bug #64638, bug #72862, bug #77935.

Closes GH-6518.

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