This PR introduces Tinted button styles and the `selected_style` field
on buttons to allow replicating the previous design of titlebar call
controls. It also updates the styles of the titlebar controls.

### Creating a tinted button:

```
Button::new("accept-cta", "Accept")
    .style(ButtonStyle::Tinted(TintColor::Accent))
    .on_click(...)
```

Ths button will always be tinted blue.

### Creating a button that becomes tinted when selected::

```rust
IconButton::new("screen-share", Icon::Screen)
    .style(ButtonStyle::Subtle)
    .selected(is_screen_sharing)
    .selected_style(ButtonStyle::Tinted(TintColor::Accent))
    .on_click(...),
```

This button will be flat/subtle by default, but be tinted blue when it
is `selected`.

Note: There appears to be some issue where `is_deafened` isn't
activating correctly, making the speaker icon not toggle when selected.

Release Notes:

- Restore call control styles to a similar look to Zed 1.