[FIR] Introduce & use toFirLightSourceElement

compiler/fir/raw-fir/light-tree2fir/src/org/jetbrains/kotlin/fir/lightTree/converter/BaseConverter.kt

@@ -12,10 +12,10 @@ import com.intellij.util.diff.FlyweightCapableTreeStructure
 import org.jetbrains.kotlin.KtNodeTypes
 import org.jetbrains.kotlin.fir.FirLightSourceElement
 import org.jetbrains.kotlin.fir.FirSession
-import org.jetbrains.kotlin.fir.FirSourceElement
 import org.jetbrains.kotlin.fir.builder.BaseFirBuilder
 import org.jetbrains.kotlin.fir.builder.Context
 import org.jetbrains.kotlin.fir.builder.escapedStringToCharacter
+import org.jetbrains.kotlin.fir.toFirLightSourceElement
 import org.jetbrains.kotlin.fir.types.builder.buildImplicitTypeRef
 import org.jetbrains.kotlin.lexer.KtToken
 import org.jetbrains.kotlin.lexer.KtTokens.*
@@ -33,7 +33,7 @@ open class BaseConverter(
     override fun LighterASTNode.toFirSourceElement(): FirLightSourceElement {
         val startOffset = offset + tree.getStartOffset(this)
         val endOffset = offset + tree.getEndOffset(this)
-        return FirLightSourceElement(this, startOffset, endOffset, tree)
+        return toFirLightSourceElement(startOffset, endOffset, tree)
     }
 
     override val LighterASTNode.elementType: IElementType

compiler/fir/tree/src/org/jetbrains/kotlin/fir/FirModifierList.kt

@@ -65,6 +65,6 @@ val FirModifier<*>.source: FirSourceElement?
             // TODO pretty sure I got offsets wrong here
             val startOffset = tree.getStartOffset(node)
             val endOffset = tree.getEndOffset(node)
-            FirLightSourceElement(node, startOffset, endOffset, tree)
+            node.toFirLightSourceElement(startOffset, endOffset, tree)
         }
     }

compiler/fir/tree/src/org/jetbrains/kotlin/fir/FirSourceElement.kt

@@ -49,6 +49,12 @@ val FirElement.psi: PsiElement? get() = (source as? FirPsiSourceElement<*>)?.psi
 @Suppress("NOTHING_TO_INLINE")
 inline fun PsiElement.toFirPsiSourceElement(): FirPsiSourceElement<*> = FirPsiSourceElement(this)
 
+@Suppress("NOTHING_TO_INLINE")
+inline fun LighterASTNode.toFirLightSourceElement(
+    startOffset: Int, endOffset: Int,
+    tree: FlyweightCapableTreeStructure<LighterASTNode>
+): FirLightSourceElement = FirLightSourceElement(this, startOffset, endOffset, tree)
+
 val FirSourceElement?.lightNode: LighterASTNode? get() = (this as? FirLightSourceElement)?.element
 
 fun FirSourceElement?.getModifierList(): FirModifierList? {