Add support for italic fonts.

Note, when this updated version is made available to IntelliJ, the following change must be made to `JBTerminalPanel`:

```java
  @Override
  protected Font getFontToDisplay(char c, TextStyle style) {
    boolean bold = style.hasOption(TextStyle.Option.BOLD);
    boolean italic = style.hasOption(TextStyle.Option.ITALIC);
    int fontStyle =
        (bold ? Font.BOLD : Font.PLAIN) |
        (italic? Font.ITALIC : Font.PLAIN);
    FontInfo fontInfo = fontForChar(c, fontStyle);
    return fontInfo.getFont();
  }
```