Minor: Standardize the separator in name

[jayzhan211]

Which issue does this PR close?

Closes #.

Rationale for this change

I got the name checking error that due to the mismatch of separator in creating name. I found that most of the name built with single comma and space, so I think we should switch others to this format.

Error is like

External error: query failed: DataFusion error: Internal error: Input field name SUM(get_field(CASE WHEN get_field(t2.struct(t1.time,t1.load1,t1.load2,t1.host), Utf8("c3")) IS NOT NULL THEN t2.struct(t1.time,t1.load1,t1.load2,t1.host) END,Utf8("c2"))) does not match with the projection expression SUM(get_field(CASE WHEN get_field(t2.struct(t1.time,t1.load1,t1.load2,t1.host),Utf8("c3")) IS NOT NULL THEN t2.struct(t1.time,t1.load1,t1.load2,t1.host) END,Utf8("c2"))).
This was likely caused by a bug in DataFusion's code and we would welcome that you file an bug report in our issue tracker
[SQL] select t2."struct(t1.time,t1.load1,t1.load2,t1.host)"['c3'] as host, sum((case when t2."struct(t1.time,t1.load1,t1.load2,t1.host)"['c3'] is not null then t2."struct(t1.time,t1.load1,t1.load2,t1.host)" end)['c2']) from (select struct(time,load1,load2,host) from t1) t2 where t2."struct(t1.time,t1.load1,t1.load2,t1.host)"['c3'] IS NOT NULL group by t2."struct(t1.time,t1.load1,t1.load2,t1.host)"['c3'] order by host;

I got one with t2.struct(t1.time,t1.load1,t1.load2,t1.host), Utf8("c3") and another t2.struct(t1.time,t1.load1,t1.load2,t1.host),Utf8("c3"). That is why I think we should fix the separator.

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

You can find the error here with cargo test --test sqllogictests -- expr. Although, it is not on the main branch, but I think most of the changes are unrelated to the name checking issue.