[META] Fix separators / decimals calculations

I was not involved in writing that code and I don't know what the original intent was for how to handle number formatting. I would have to first try to reproduce this problem then figure out what to do about it. Usually, formatting numbers would be something done as late as possible, because this is essentially just theming/presentation and could differ on a per-user/per-page/per-view basis.

Since you already have a site set up that uses a different number format, you are in a better position to create a test case that demonstrates the problem. That is the first step in finding a solution. If you can do that, it would go a long way towards getting this fixed.

MR36 fixes the issues with number formatting with decimals/commas: https://www.drupal.org/project/views_aggregator/issues/3482129

To test, I added a decimal field to the article content type in the standard install profile, and generated content with devel generate.

Then I created a view that lists article titles and the decimal field, formatted with views aggregator.

Group sum:

Column sum:

There are a handful of options to test, like enabling prefix/suffix, which is configured in the field settings.

For me it works great out of the box! I am only using the patch from https://git.drupalcode.org/project/views_aggregator/-/merge_requests/37

I adjusted my decimal fields view settings to have the "decimal dot" as the "thousand separator", and a "comma" as my "decimal point" representation and the output is as expected (including the sum):

To be fair I don't do any complex calculation or grouping, so there might be still issues when displaying decimal numbers.