DDC-3717: [GH-1397] Add Expr::concat support for multiple arguments

[doctrinebot]

Jira issue originally created by user @doctrinebot:

This issue is created automatically through a Github pull request on behalf of giosh94mhz:

Url: #1397

Message:

DQL CONCAT function support variable number of arguments (2+) since version 2.4.0.

The Expr class, on the other hand, is still limited to 2 arguments, and require multiple call to achive a similar result (see this SO question). I've improved Expr implementation to support variable number of arguments in a backward compatible way.

Please, consider backporting to 2.4 branch if you plan to release other versions, since 2.5 introduce many features and may not be possible to easily upgrade. I may be wrong, though.

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-1397] was labeled:
#1397

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-1397] was assigned:
#1397

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-1397] was unassigned:
#1397

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-1397] was unlabeled:
#1397

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-1397] was merged:
#1397

[doctrinebot]

Issue was closed with resolution "Fixed"

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-1397] was unassigned:
#1397

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-1397] was assigned:
#1397