DataGrid - Fix remaining theme colors

[Symbai]

What does the pull request do?

Replace remaining hardcoded brushes with theme brushes. I had to use similar theme brush values because the hardcoded brush values don't exist in theme resource dictionary.

Before Light

After Light

Before Dark

After Dark

[grokys]

@Symbai I've just noticed that #3530 causes a problem: the row highlight color is now the same as the TextBox highlight color, so when you double-click to edit a DataGridTextColumn, you can't see that the text is highlighted, for example:

I think we need to choose a different color for the row highlight, could we do that in this PR? Here's the above operation using ThemeAccentBrush (which might be a good choice?) for example:

Other than that, PR looks good!

[Symbai]

@grokys Nice catch. Using ThemeAccentBrush makes the selection really noticeably. But on dark theme it barely is then:

Light

Dark

How about ThemeAccentBrush2?

Light:

Dark:

[Gillibald]

Can't we change the background of the TextBox so it does not have the same color as the selected row?

[Symbai]

@Gillibald Generally we should consider adding background colors to many controls as currently many controls have a transparent background, causing the issue above (different behavior to WPF and causes issues when controls are placed on a custom background. I wanted to make a PR someday later about).

In WPF the textbox in DataGrid has a background which is not transparent, matching with your suggestion.

If this is what we want to do, I would undo the change in this PR and make a new PR setting background colors to several controls.

[grokys]

Hmm yeah maybe that would be better, if that's what WPF does. If that's the case 👍 to reverting the change there.

[Symbai]

Done