[LL FIR] rewrote in-block modifications logic

Now we will invalidate bodies for FIR declarations
immediately after in-block modifications in these declarations
We assume that such in-block modifications can happen
only under write action,
so it should be safe to make changes for FirFile

^KT-59687 Fixed
^KT-59199 Fixed
^KTIJ-26066 Fixed

analysis/low-level-api-fir/testdata/inBlockModification/memberFunWithBodyWithContract.kt

@@ -0,0 +1,13 @@
+import kotlin.contracts.contract
+
+class A {
+    fun <caret>x() {
+        contract {
+            req
+        }
+
+        val a = doSmth("str")
+    }
+}
+
+fun doSmth(i: String) = 4