[LL FIR] add missed ClassId check for combined Java classes symbol provider

findClasses works over regular `PsiElementFinder`, which doesn't know
about out ClassId conception. So, `a/b/A.B` and `a/b/A/B` are the same
from `FqName` point of view.
`FirJavaFacade` has this check, so this problem appears only in the case
of combined provider.

^KT-62892 Fixed

analysis/low-level-api-fir/testData/getOrBuildFir/types/nestedClassFromJava.txt

@@ -3,11 +3,11 @@ FIR element: FirResolvedTypeRefImpl
 FIR source kind: KtRealSourceElementKind
 
 FIR element rendered:
-R|issue/pack/RowIcon/RClass|
+R|issue/pack/RowIcon.RClass|
 
 FIR FILE:
 FILE: [ResolvedTo(IMPORTS)] usage.kt
     package usage
 
-    public final [ResolvedTo(ANNOTATION_ARGUMENTS)] fun testJavaNestedClass([ResolvedTo(ANNOTATION_ARGUMENTS)] alignment: R|issue/pack/RowIcon/RClass|): R|kotlin/Unit| {
-    }
+    public final [ResolvedTo(ANNOTATION_ARGUMENTS)] fun testJavaNestedClass([ResolvedTo(ANNOTATION_ARGUMENTS)] alignment: R|issue/pack/RowIcon.RClass|): R|kotlin/Unit| {
+    }