Bind to EnvironmentFontFamily in DocumentOutLineWindow.

[Cosifne]

Fix #68809
It is needed because we need the ability to display GB18030.
In order to display it, OullineWindow must be able to change the font, since not all the font supports the character set.
After the change, all the character can be displayed:

Several problems in the existing code.

1. Currently DocumentOutlineWindow is wrapped in a Windows form control in order to get the handle and send it back to shell.

   roslyn/src/VisualStudio/Core/Def/LanguageService/AbstractLanguageService`2.VsCodeWindowManager.cs

   Line 277 in 575bc42

   _documentOutlineViewHost = new ElementHost

   
   I don't know a lot about WinForm but it doesn't inherit the property from the parent like in WPF.
   Like:
   The child font doesn't match its parent font

In this case, all the elements (except the one with font-family property) in the window would inherit from the windows form control. And I don't find there is a way to change this.

2. We only set Font for TreeView and TextBox now. This feels wrong since the tool window might have SearchTextBox.

3. The Font used is vsshell:VsFonts.CaptionFontFamilyKey, I don't know what it means in the shell. But from what I understand here, this is the font used in VS title bar. I don't feel it is meaningful to keep the font here the same as the Title bar.

[sharwell]

We only set Font for TreeView and TextBox now. This feels wrong since the tool window might have SearchTextBox.

The search box is a platform control, not implemented or provided by us. This change was implemented in #68094.

[Cosifne]

We only set Font for TreeView and TextBox now. This feels wrong since the tool window might have SearchTextBox.

The search box is a platform control, not implemented or provided by us. This change was implemented in #68094.

What I mean is we need to have a way to change the text font in the search text box.
From there we just make sure all the TreeView and TextBox would have the correct font.
If we specify the font at DocumentViewOutline control level, all the child element of it would inherited the property (if it is not specified), which solves our problem.

[Cosifne]

Also tag Andrew to review @ryzngard