Fix TJSProgressEvent.Total to refer to lowecase `total` in JS

The TJSProgressEvent.FTotal field refers to JS Total, it should be total instead. Only the lowercase version matches the field on the JS side.

This is useful to show nice progress when using TJSXMLHttpRequest, getting event's loaded / total, as long as HTTP server sends content length in response (so total is known before we receive the file). We use this in CGE to show progress of downloading game data, before the fix the progress cannot show anything useful as Total is undefined.

I don't have a simple testcase (independent from CGE) now, let me know if you need it.

I also tried to use regexp (case-sensitive) to find possible other occurrences of such mistake, when field name in pas2js has "external name" that starts with an uppercase letter:

^    F[^u].*external name '[A-Z]

See screenshot below. This regexp found a lot of cases when it is actually correct, but I think it found one other occurrence that needs fixing too, in TJSWindow :

FPerformance: TJSPerformance; external name 'Performance';

I think this should be lowercase performance, at least MDN says it's lowercase. But I don't have 100% confidence / a testcase for this now, so this PR doesn't change it. I mention it here for consideration.