GuessManagerImpl: do not run DFA if all assignments/initializations have the same r-value type

Fixes IDEA-185290 Too long time takes filling of Ctrl+Space list. (fast code insertion)

java/java-tests/testData/codeInsight/completion/normal/AssignmentNoPreciseTypeDfa.java

@@ -0,0 +1,9 @@
+class Foo {
+    void test(boolean b) {
+        List<String> list = new ArrayList<>();
+        if (b) {
+            list = Collections.emptyList();
+        }
+        System.out.println(list.trimTo<caret>);
+    }
+}

java/java-tests/testData/codeInsight/completion/normal/AssignmentNoPreciseTypeDfa_after.java

@@ -0,0 +1,9 @@
+class Foo {
+    void test(boolean b) {
+        List<String> list = new ArrayList<>();
+        if (b) {
+            list = Collections.emptyList();
+        }
+        System.out.println(list.trimTo);
+    }
+}