RadzenDataFilter numeric input fixes

[kerajel]

I wish there was a better way to fix these issues, but since the numeric input relies on the 'onchange' event and not on the 'oninput' event it's hard to come up with something. If there is a better way to force an input to 'commit' its changes into the 'onchange' event on demand, it'd be best to use it, but I am not aware of other solutions.

Resolving #1818
blurAllNumericInputs - this functions should be called from client's code right before you want to read RadzenDataFilter<>.ToFilterString();

Resolving #1842
Reference the new OnFilterOperatorChanged method (its logic was inlined before). The loss of values occurs at the await InvokeAsync(ChangeState); because the 'onchange' event of the corresponding numeric input has not committed and server-side DOM is not aware of user's input. Temporarily stashing the current input values and then restoring them resolves the issue. Other blurring techniques did not work in this case.

[enchev]

I don't think that we should merge this code - the DataGrid filtering should not mess with all input components in the current page in first place. I still believe that handling internally oninput is the only reliable way to avoid such problems with Blazor server lag:
124033d

[kerajel]

@enchev, but how would I handle the 'oninput' if the numeric input uses 'onchange'?

[enchev]

Check the code I’ve linked. Both can coexist.

[enchev]

Here is what I'm referring:
1a40da9