Add fill Emphasis Style Option (#120)

### Description

Adds an option to fill in the color emphasis style.

### Related Issues

* N/A

### Checklist

- [x] I read and understood the [contributing guide](https://github.com/CodeEditApp/CodeEdit/blob/main/CONTRIBUTING.md) as well as the [code of conduct](https://github.com/CodeEditApp/CodeEdit/blob/main/CODE_OF_CONDUCT.md)
- [x] The issues this PR addresses are related to each other
- [x] My changes generate no new warnings
- [x] My code builds and runs on my machine
- [x] My changes are all related to the related issue above
- [x] I documented my code

### Screenshots

N/A

Author: thecoolwinter

Sources/CodeEditTextView/EmphasisManager/EmphasisManager.swift

@@ -233,11 +233,11 @@ public final class EmphasisManager {
             layer.fillColor = nil
             layer.opacity = emphasis.flash ? 0.0 : 1.0
             layer.zPosition = 1
-        case .outline(let color):
+        case let .outline(color, shouldFill):
             layer.cornerRadius = 2.5
             layer.borderColor = color.cgColor
             layer.borderWidth = 0.5
-            layer.fillColor = nil
+            layer.fillColor = shouldFill ? color.cgColor : nil
             layer.opacity = emphasis.flash ? 0.0 : 1.0
             layer.zPosition = 1
         }

Sources/CodeEditTextView/EmphasisManager/EmphasisStyle.swift

@@ -14,16 +14,16 @@ public enum EmphasisStyle: Equatable {
     /// Underline emphasis with a line color
     case underline(color: NSColor)
     /// Outline emphasis with a border color
-    case outline(color: NSColor)
+    case outline(color: NSColor, fill: Bool = false)
 
     public static func == (lhs: EmphasisStyle, rhs: EmphasisStyle) -> Bool {
         switch (lhs, rhs) {
         case (.standard, .standard):
             return true
         case (.underline(let lhsColor), .underline(let rhsColor)):
             return lhsColor == rhsColor
-        case (.outline(let lhsColor), .outline(let rhsColor)):
-            return lhsColor == rhsColor
+        case let (.outline(lhsColor, lhsFill), .outline(rhsColor, rhsFill)):
+            return lhsColor == rhsColor && lhsFill == rhsFill
         default:
             return false
         }

Sources/CodeEditTextView/TextView/TextView.swift

@@ -33,7 +33,7 @@ import TextStory
 /// [`NSTextInputClient`](https://developer.apple.com/documentation/appkit/nstextinputclient) to work well with system
 /// text interactions such as inserting text and marked text.
 ///
-public class TextView: NSView, NSTextContent {
+open class TextView: NSView, NSTextContent {
     // MARK: - Statics
 
     /// The default typing attributes:
@@ -356,7 +356,7 @@ public class TextView: NSView, NSTextContent {
         setUpDragGesture()
     }
 
-    required init?(coder: NSCoder) {
+    required public init?(coder: NSCoder) {
         fatalError("init(coder:) has not been implemented")
     }