[LL FIR] rename testdata to testData to avoid copyright generation

We exclude testData pattern from copyright scope

analysis/low-level-api-fir/testData/getOrBuildFir/inImport/middleImportNamePart.txt

@@ -0,0 +1,9 @@
+KT element: KtNameReferenceExpression
+FIR element: FirImportImpl
+FIR source kind: KtRealSourceElementKind
+
+FIR element rendered:
+import a.b.c
+
+FIR FILE:
+FILE: [ResolvedTo(IMPORTS)] middleImportNamePart.kt