FIR CFG: when unifying flows, group statements by assignment

Consider a function `run2` that has 2 lambda arguments called in place.
We don't know the order in which they're called, so here:

    var x: Any? = something
    run2(
      { x = null },
      { x as String },
    )
    // <--

it's not correct to simply `&&` the statements together, as that would
produce `x is Nothing? && x is String && x is Any?`. Instead, statements
should be grouped by assignment first, and different groups are `||`-ed.
This means in the above example we now get `x is Nothing? || (x is Any?
&& x is String)` == `x is String?`.

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerFirTestdataTestGenerated.java

@@ -1083,6 +1083,12 @@ public class DiagnosisCompilerFirTestdataTestGenerated extends AbstractDiagnosis
                 runTest("compiler/fir/analysis-tests/testData/resolve/cfg/flowFromInplaceLambda2.kt");
             }
 
+            @Test
+            @TestMetadata("flowFromTwoInplaceLambdas.kt")
+            public void testFlowFromTwoInplaceLambdas() throws Exception {
+                runTest("compiler/fir/analysis-tests/testData/resolve/cfg/flowFromTwoInplaceLambdas.kt");
+            }
+
             @Test
             @TestMetadata("initBlock.kt")
             public void testInitBlock() throws Exception {