Gradual migration of operator 'mod' to 'rem'

- Introduce new 'rem' operator convention
 - Prefer 'rem()' to 'mod()' when both are available, even if mod() is a
   member, and rem() -- an extension
 - Place operator 'rem' under the language feature

compiler/testData/diagnostics/tests/operatorRem/noOperatorRemFeature.kt

@@ -0,0 +1,16 @@
+// !LANGUAGE: -OperatorRem
+// !DIAGNOSTICS: -UNUSED_PARAMETER, -UNUSED_VARIABLE
+
+class Foo {
+    <!UNSUPPORTED_FEATURE!>operator<!> fun rem(x: Int): Foo = Foo()
+}
+
+class Bar {
+    <!UNSUPPORTED_FEATURE!>operator<!> fun remAssign(x: Int) {}
+}
+
+fun baz() {
+    val f = Foo() % 1
+    val b = Bar()
+    b %= 1
+}

compiler/testData/diagnostics/tests/operatorRem/noOperatorRemFeature.txt

@@ -0,0 +1,19 @@
+package
+
+public fun baz(): kotlin.Unit
+
+public final class Bar {
+    public constructor Bar()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final operator fun remAssign(/*0*/ x: kotlin.Int): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class Foo {
+    public constructor Foo()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final operator fun rem(/*0*/ x: kotlin.Int): Foo
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/operatorRem/operatorRem.kt

@@ -0,0 +1,15 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER, -UNUSED_VARIABLE
+
+class Foo {
+    operator fun rem(x: Int): Foo = Foo()
+}
+
+class Bar {
+    operator fun remAssign(x: Int) {}
+}
+
+fun baz() {
+    val f = Foo() % 1
+    val b = Bar()
+    b %= 1
+}

compiler/testData/diagnostics/tests/operatorRem/operatorRem.txt

@@ -0,0 +1,19 @@
+package
+
+public fun baz(): kotlin.Unit
+
+public final class Bar {
+    public constructor Bar()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final operator fun remAssign(/*0*/ x: kotlin.Int): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class Foo {
+    public constructor Foo()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final operator fun rem(/*0*/ x: kotlin.Int): Foo
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/operatorRem/preferRemAsExtentionOverMod.kt

@@ -0,0 +1,12 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+class Foo {
+}
+operator fun Foo.mod(x: Int): Foo = Foo()
+operator fun Foo.rem(x: Int): Int = 0
+
+fun foo() {
+    takeInt(Foo() % 1)
+}
+
+fun takeInt(x: Int) {}

compiler/testData/diagnostics/tests/operatorRem/preferRemAsExtentionOverMod.txt

@@ -0,0 +1,13 @@
+package
+
+public fun foo(): kotlin.Unit
+public fun takeInt(/*0*/ x: kotlin.Int): kotlin.Unit
+public operator fun Foo.mod(/*0*/ x: kotlin.Int): Foo
+public operator fun Foo.rem(/*0*/ x: kotlin.Int): kotlin.Int
+
+public final class Foo {
+    public constructor Foo()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/operatorRem/preferRemAsMemberOverMod.kt

@@ -0,0 +1,12 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+class Foo {
+    operator fun mod(x: Int): Foo = Foo()
+    operator fun rem(x: Int): Int = 0
+}
+
+fun foo() {
+    takeInt(Foo() % 1)
+}
+
+fun takeInt(x: Int) {}

compiler/testData/diagnostics/tests/operatorRem/preferRemAsMemberOverMod.txt

@@ -0,0 +1,13 @@
+package
+
+public fun foo(): kotlin.Unit
+public fun takeInt(/*0*/ x: kotlin.Int): kotlin.Unit
+
+public final class Foo {
+    public constructor Foo()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final operator fun mod(/*0*/ x: kotlin.Int): Foo
+    public final operator fun rem(/*0*/ x: kotlin.Int): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/operatorRem/prefereRemAsExtensionOverMemberMod.kt

@@ -0,0 +1,14 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+class Foo {
+    operator fun mod(x: Int): Foo = Foo()
+}
+
+operator fun Foo.rem(x: Int): Int = 0
+
+
+fun foo() {
+    takeInt(Foo() % 1)
+}
+
+fun takeInt(x: Int) {}

compiler/testData/diagnostics/tests/operatorRem/prefereRemAsExtensionOverMemberMod.txt

@@ -0,0 +1,13 @@
+package
+
+public fun foo(): kotlin.Unit
+public fun takeInt(/*0*/ x: kotlin.Int): kotlin.Unit
+public operator fun Foo.rem(/*0*/ x: kotlin.Int): kotlin.Int
+
+public final class Foo {
+    public constructor Foo()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final operator fun mod(/*0*/ x: kotlin.Int): Foo
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}