Bug 64633

Created attachment 37377 [details]
Implementation of TEXTJOIN

TEXTJOIN was added to Excel in 2016.  It's used to concatenate strings with a specified delimiter, and to optionally exclude arguments evaluating as empty:

https://support.microsoft.com/en-us/office/textjoin-function-357b449a-ec91-49d0-80c3-0e8fc845691c

The attached patch adds support for the TEXTJOIN function, as well as a suite of unit tests for it.

First time submitting a POI patch, so please let me know if I've done something incorrectly and I'm happy to fix it!  Specifically, I wasn't sure the best way to bind the new function class to the function name, so I cribbed off another patch that added a new function via a binding in AnalysisToolPak.createFunctionsMap.

The patch was created against trunk, but for my own project's use, I've applied it back to 4.1.2, and that seems to work fine as well.

See also bug 60924.  I filed this separately in the interest of an easy merge since that one is a fairly old open bug with many functions listed, but if it's better to include it in there, that works too.