Support VARCHAR /VARVHAR(N)Type in hyrbidse

[jingchen2222]

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CREATE table t1 (
c1 int not null,
c2 varchar not null,
c3 varchar(64) not null,
c4 timestamp not null,
index(key=c1, ts=c4)
);

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[jingchen2222]

Resolve 4paradigm/HybridSE#193