[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/nullabilityOperations.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_EXPRESSION -UNUSED_PARAMETER -UNUSED_VARIABLE -NOTHING_TO_INLINE -ASSIGNED_BUT_NEVER_ACCESSED_VARIABLE -UNUSED_VALUE -UNNECESSARY_SAFE_CALL -UNNECESSARY_NOT_NULL_ASSERTION -CONFLICTING_JVM_DECLARATIONS
 inline fun String.submit(action: Function1<Int, Int>) {
 
@@ -13,4 +14,4 @@ inline fun Function1<Int, Int>.submit() {
 inline fun submit(action: Function1<Int, Int>) {
     <!USAGE_IS_NOT_INLINABLE!>action<!>?.invoke(10)
     <!USAGE_IS_NOT_INLINABLE!>action<!>!!.invoke(10)
-}
+}