Change error message when INSTANT ADD/DROP not possible in max column count

Background:
When a table with max column (1017) has repeated instant drop
followed by instant add on the same column, the n_def parameter
increases. This parameter has a max limit of 1023. Hence when we
cross this limit, the server reports "Too many columns".

Problem:
The error message from the server is misleading and columns
can't be added with ALGORITHM=INSTANT only. We can still
add column using INPLACE or COPY algorithm.

首先，在具有所述最大列数的表上复现重复的即时 DROP 后紧接即时 ADD，然后检查服务器针对 ALGORITHM=INSTANT 报告 "Too many columns" 的位置。将其行为与 INPLACE 和 COPY 进行比较，并确认由此产生的错误解释了该算法的限制，而这些替代方案仍然可用。