fix syntax highlighting and variable highlighting were gone

src/jvmMain/kotlin/com/sunnychung/application/multiplatform/hellohttp/ux/bigtext/BigText.kt

@@ -49,7 +49,7 @@ interface BigText {
 
     fun substring(range: IntRange): CharSequence = substring(range.start, range.endInclusive + 1)
 
-    fun subSequence(startIndex: Int, endIndex: Int) = substring(startIndex, endIndex)
+    fun subSequence(startIndex: Int, endIndex: Int): CharSequence
 
     fun findLineString(lineIndex: Int): CharSequence
 

src/jvmMain/kotlin/com/sunnychung/application/multiplatform/hellohttp/ux/bigtext/ConcurrentBigText.kt

@@ -61,6 +61,8 @@ open class ConcurrentBigText(private val delegate: BigText) : BigText {
 
     override fun substring(start: Int, endExclusive: Int): CharSequence = lock.read { delegate.substring(start, endExclusive) }
 
+    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence = lock.read { delegate.subSequence(startIndex, endIndex) }
+
     override fun findLineString(lineIndex: Int): CharSequence = lock.read { delegate.findLineString(lineIndex) }
 
     override fun findRowString(rowIndex: Int): CharSequence = lock.read { delegate.findRowString(rowIndex) }

src/jvmMain/kotlin/com/sunnychung/application/multiplatform/hellohttp/ux/bigtext/InefficientBigText.kt

@@ -61,6 +61,9 @@ class InefficientBigText(text: String) : BigText {
     override fun substring(range: IntRange): CharSequence =
         substring(range.first, range.last)
 
+    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence =
+        substring(startIndex, endIndex)
+
     override fun findLineString(lineIndex: Int): CharSequence {
         TODO("Not yet implemented")
     }