Fuse primitive equality with safe call to avoid boxing

In code like 'a?.b == 42', we can immediately generate equality
comparison result when receiver is null (false for '==', true for '!='),
since the primitive value is definitely non-null.
Otherwise unnecessary boxing/unboxing is generated to handle possibly
null result of 'a?.b'.

compiler/testData/codegen/box/safeCall/primitiveEqSafeCall.kt

@@ -0,0 +1,56 @@
+fun Long.id() = this
+
+fun String.drop2() = if (length >= 2) subSequence(2, length) else null
+
+fun String.anyLength(): Any = length
+
+
+fun doSimple(s: String?) = 3 == s?.length
+
+fun doLongReceiver(x: Long) = 3L == x?.id()
+
+fun doChain(s: String?) = 1 == s?.drop2()?.length
+
+fun doIf(s: String?) =
+        if (1 == s?.length) "A" else "B"
+
+fun doCmpWithAny(s: String?) =
+        3 == s?.anyLength()
+
+fun doIfNot(s: String?) =
+        if (!(1 == s?.length)) "A" else "B"
+
+fun doIfNotNot(s: String?) =
+        if (!!(1 == s?.length)) "A" else "B"
+
+
+fun box(): String = when {
+    doSimple(null) -> "failed 1"
+    doSimple("1") -> "failed 2"
+    !doSimple("123") -> "failed 3"
+
+    doLongReceiver(2L) -> "failed 4"
+    !doLongReceiver(3L) -> "failed 5"
+
+    doChain(null) -> "failed 6"
+    doChain("1") -> "failed 7"
+    !doChain("123") -> "failed 7"
+
+    doIf("1") != "A" -> "failed 8"
+    doIf("123") != "B" -> "failed 9"
+    doIf(null) != "B" -> "failed 10"
+
+    doCmpWithAny(null) -> "failed 11"
+    doCmpWithAny("1") -> "failed 12"
+    !doCmpWithAny("123") -> "failed 13"
+
+    doIfNot("1") != "B" -> "failed 8"
+    doIfNot("123") != "A" -> "failed 9"
+    doIfNot(null) != "A" -> "failed 10"
+
+    doIfNotNot("1") != "A" -> "failed 8"
+    doIfNotNot("123") != "B" -> "failed 9"
+    doIfNotNot(null) != "B" -> "failed 10"
+
+    else -> "OK"
+}