[FIR] Add inline checker for bodies of inline functions

This checker doesn't support `@PublishedAPI` yet, so some BB tests for it
 were muted. #KT-46270

compiler/testData/diagnostics/tests/inline/assignment.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_EXPRESSION -UNUSED_PARAMETER -UNUSED_VARIABLE -NOTHING_TO_INLINE -ASSIGNED_BUT_NEVER_ACCESSED_VARIABLE -UNUSED_VALUE
 inline fun inlineFunWithInvoke(s: (p: Int) -> Unit, ext: Int.(p: Int) -> Unit) {
     var d = <!USAGE_IS_NOT_INLINABLE!>s<!>
@@ -11,4 +12,4 @@ inline fun inlineFunWithInvoke(s: (p: Int) -> Unit, ext: Int.(p: Int) -> Unit) {
 inline fun Function1<Int, Unit>.inlineExt() {
     var d = this
     d = this
-}
+}