fix: #992 do not localize numbers in csv

[hexaltation]

Fix #992

Numbers should not be localized.
French float numbers representation was "1,234" in csv now its 1.234.

It makes it simpler for many other softwares to guess correctly data type when importing csv generated by grist.

[fflorent]

Modulo the code formatting and the CI result, LGTM

[hexaltation]

This draft was to run tests that I can't run locally.

Modulo the code formatting and the CI result, LGTM

Test fails are legitimate.

Replacing

   public _formatPlain(value: number): string {
-    return this._numFormat.format(value);
+    return String(value);
   }

leads to some wanted identities fail :

***
(1) ClientUnitTests.ntest should reach 100% with no failures
Error: Browser returned 6 failed tests:
ValueFormatter NumericFormatter should support plain format: AssertionError: expected 'Infinity' to equal '∞'
ValueFormatter NumericFormatter should support min/max decimals: AssertionError: expected '12' to equal '12.00'
ValueFormatter NumericFormatter should support thousand separators: AssertionError: expected '1000000' to equal '1,000,000.0000'
ValueFormatter NumericFormatter should support currency mode: AssertionError: expected '1000000' to equal '$1,000,000.00'
ValueFormatter NumericFormatter should support percentages: AssertionError: expected '0.5' to equal '50%'
ValueFormatter NumericFormatter should support scientific mode: AssertionError: expected '0.5' to equal '5E-1'
    at Context.<anonymous> (test/nbrowser/ClientUnitTests.ntest.js:21:13)
    at processTicksAndRejections (node:internal/process/task_queues:95:5)
***

[hexaltation]

I think that a better Idea than previous one is to force locals to en-US for decimal in Intl.NumberFormat() "decimal" (default)
(only ?) in case of dsv export.

[dsagal]

I am not sure that your change affects only csv exports (does it not affect the main UI?) But even for CSV, see my comment here: #992 (comment). In short, it's an intentional choice to export numbers in the same format as what you see on the screen, and it's consistent with other produces (Excel/Google Sheets), and other operations (copy-pasting). If having an "unformatted" output like this is important, I think we'd need to provide an option for the user to choose the behavior.