[CmdPal][Calc]Parse result returned by ExprTk correctly (#40317)

## Summary of the Pull Request
The ExprTk result was previously parsed with CurrentCulture, which means
that calculator was broken on every device which's culture info differed
from what ExprTk returns.
It would probably be better to just obtain the result as a double
directly, but that can wait.
## PR Checklist
- [x] **Closes:** #40305
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [x] **Localization:** All end-user-facing strings can be localized
- [x] **Dev docs:** No need
- [x] **New binaries:** None
- [x] **Documentation updated:** No need

## Detailed Description of the Pull Request / Additional comments
ExprTk, the math library that CmdPal's Calculator uses, returns the
result as a string formatted in `en-US`, therefore we need to also parse
it as `en-US`.
## Validation Steps Performed
Small and large numbers work correctly with all decimal separators

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.Calc/Helper/CalculateEngine.cs

@@ -82,7 +82,7 @@ public static class CalculateEngine
             return default;
         }
 
-        var decimalResult = Convert.ToDecimal(result, cultureInfo);
+        var decimalResult = Convert.ToDecimal(result, new CultureInfo("en-US"));
 
         var roundedResult = FormatMax15Digits(decimalResult, cultureInfo);