Fix issue where ignore-whitespace can't be toggled (#2435)

[goran-w]

Also move the toggle-button to avoid having it jumping around when toggled (which is a UI-design no-no).

This fixes issue #2435.

(Additionally, renamed nearby variable from _entireFileLine to _entireFileLines, for clarity and consistency with variable _unifiedLines.)

[love-linger]

• Please run dotnet format src/SourceGit.csproj first
• I'd like to change the CheckSettings to

var pref = Preferences.Instance;

if (Content is TextDiffContext ctx)
{
    if ((pref.UseFullTextDiff && _info.UnifiedLines != _entireFileLine) ||
        (!pref.UseFullTextDiff && _info.UnifiedLines == _entireFileLine) ||
        (pref.IgnoreWhitespaceChangesInDiff != _info.IgnoreWhitespace))
    {
        LoadContent();
        return;
    }

    if (ctx.IsSideBySide() != pref.UseSideBySideDiff)
        Content = ctx.SwitchMode();
}
else if (Content is Models.NoOrEOLChange)
{
    if (pref.IgnoreWhitespaceChangesInDiff != _info.IgnoreWhitespace)
        LoadContent();
}

[goran-w]

• Please run dotnet format src/SourceGit.csproj first

Fixed. But could we have this format step run automatically when building in Visual Studio? It's annoying when a PR check fails because of a missed step that could've been automated...

• I'd like to change the CheckSettings to

Done.

[love-linger]

But could we have this format step run automatically when building in Visual Studio? It's annoying when a PR check fails because of a missed step that could've been automated

I'm not sure if we add some pre-build task will work for all IDEs. Instead, before I push something to this repository, I'll run a custom action to do this job.