Bug #86579 Table data export wizard is VERY SLOW exporting "large" datasets

Description:
Workbench is very slow exporting large datasets through the CSV export wizard. Disproportionately slow comapred to a smaller set. However, this is something I've come across before with .NET.

How to repeat:
Get a table with 15k or so records or more, and export through the wizard. Note how long it takes and then export a subset of that data and see how the time taken does not correlate linearly with the amount of rows. 

Suggested fix:
Something I've noticed when building CSV export applications is that the MS .NET framework can't deal with huge strings very well, and tends to perform badly as a result.

I found a solution though. When building up the huge string to the dump into the file when you've done generating it, instead of building 1 huge string and writing it to file all at once when the export is done, I get much better performance by only doing a few hundred rows of CSV generated at a time, write it to the file and flush the buffer you have been writing the generated data to. 

I'd recommend writing to a temp file, then rename/move it to the user's specified one when done. The Write to temp and then move/rename is the way Photoshop and some other applications save their data. And the writing x rows and flushing I've found when developing myself is much faster than trying to get .NET to manage a 20MB string.

Thank you for the bug report. Duplicate/related to https://bugs.mysql.com/bug.php?id=86430.