kotlin-extractor: converge backing-field locations across language versions

Anchor a property backing field's location on its property declaration (the
`val`/`var` keyword to the end of the declaration) rather than the raw IR
offset. The raw `IrField` offset is inconsistent between frontends: under
`-language-version 1.9` it includes leading modifiers in the span start, while
under 2.0 it starts at the `val`/`var` keyword.

Example: `private val privateProp: Int = 0`

  before (lang 1.9):  properties.kt:35:5:35:32  | int privateProp;  (col 5 = `private`)
  after  (lang 1.9):  properties.kt:35:13:35:32 | int privateProp;  (col 13 = `val`)
  lang 2.0 (unchanged): properties.kt:35:13:35:32 | int privateProp;

The property entity already uses this PSI-based anchor (getPsiBasedLocation),
so the field now matches its own property location, which is what the 2.0
frontend already emits.

Delegated properties are excluded via `isDelegated`: their field is the
`$delegate` storage, whose location is the delegate expression rather than the
property declaration, and is converged separately.

This is a no-op for `-language-version 2.0` (only test-kotlin1 expected files
change); the two suites' backing-field and field-type-access locations now
agree.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

java/kotlin-extractor/src/main/kotlin/KotlinFileExtractor.kt

@@ -2594,12 +2594,24 @@ open class KotlinFileExtractor(
                     if (isAnnotationClassField(f)) kClassToJavaClass(f.type) else f.type
                 val id = useField(f)
                 extractAnnotations(f, id, extractAnnotationEnumTypeAccesses)
+                // A plain backing field's location should match its property's location
+                // (the `val`/`var` keyword to the end of the declaration), rather than the
+                // raw IR offset, which includes leading modifiers under -language-version
+                // 1.9 but not 2.0. Anchoring on the property keeps the two consistent.
+                // Delegated properties are excluded: their field is the `$delegate` storage,
+                // whose location is the delegate expression, not the property declaration.
+                val locId =
+                    f.correspondingPropertySymbol
+                        ?.owner
+                        ?.takeUnless { it.isDelegated }
+                        ?.let { getPsiBasedLocation(it) }
+                        ?: tw.getLocation(f)
                 return extractField(
                     id,
                     "${f.name.asString()}$fNameSuffix",
                     extractType,
                     parentId,
-                    tw.getLocation(f),
+                    locId,
                     f.visibility,
                     f,
                     isExternalDeclaration(f),