Support platform/impl modifiers for properties

Do not allow platform properties to have backing fields, initializers, be
delegated, lateinit or const, or have accessors with bodies

compiler/testData/diagnostics/tests/multiplatform/topLevelProperty/differentKindsOfProperties.kt

@@ -0,0 +1,40 @@
+// !LANGUAGE: +MultiPlatformProjects
+// MODULE: m1-common
+// FILE: common.kt
+
+platform val justVal: String
+platform var justVar: String
+
+platform val String.extensionVal: Unit
+platform var <T> T.genericExtensionVar: T
+
+platform val valWithGet: String
+    get
+platform var varWithGetSet: String
+    get set
+
+platform var varWithPlatformGetSet: String
+    <!WRONG_MODIFIER_TARGET!>platform<!> get
+    <!WRONG_MODIFIER_TARGET!>platform<!> set
+
+platform val backingFieldVal: String = <!PLATFORM_PROPERTY_INITIALIZER!>"no"<!>
+platform var backingFieldVar: String = <!PLATFORM_PROPERTY_INITIALIZER!>"no"<!>
+
+platform val customAccessorVal: String
+    <!PLATFORM_DECLARATION_WITH_BODY!>get()<!> = "no"
+platform var customAccessorVar: String
+    <!PLATFORM_DECLARATION_WITH_BODY!>get()<!> = "no"
+    <!PLATFORM_DECLARATION_WITH_BODY!>set(value)<!> {}
+
+platform <!CONST_VAL_WITHOUT_INITIALIZER!>const<!> val constVal: Int
+
+platform <!WRONG_MODIFIER_TARGET!>lateinit<!> var lateinitVar: String
+
+<!WRONG_MODIFIER_TARGET!>platform<!> val delegated: String by Delegate
+object Delegate { operator fun getValue(x: Any?, y: Any?): String = "" }
+
+fun test(): String {
+    <!WRONG_MODIFIER_TARGET!>platform<!> val localVariable: String
+    localVariable = "no"
+    return localVariable
+}

compiler/testData/diagnostics/tests/multiplatform/topLevelProperty/differentKindsOfProperties.txt

@@ -0,0 +1,25 @@
+package
+
+public val backingFieldVal: kotlin.String = "no"
+public var backingFieldVar: kotlin.String
+public const val constVal: kotlin.Int
+public val customAccessorVal: kotlin.String
+public var customAccessorVar: kotlin.String
+public val delegated: kotlin.String
+public val justVal: kotlin.String
+public var justVar: kotlin.String
+public lateinit var lateinitVar: kotlin.String
+public val valWithGet: kotlin.String
+public var varWithGetSet: kotlin.String
+public var varWithPlatformGetSet: kotlin.String
+public val kotlin.String.extensionVal: kotlin.Unit
+public var </*0*/ T> T.genericExtensionVar: T
+public fun test(): kotlin.String
+
+public object Delegate {
+    private constructor Delegate()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public final operator fun getValue(/*0*/ x: kotlin.Any?, /*1*/ y: kotlin.Any?): kotlin.String
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/multiplatform/topLevelProperty/simplePlatformVar.kt

@@ -0,0 +1,12 @@
+// !LANGUAGE: +MultiPlatformProjects
+// MODULE: m1-common
+// FILE: common.kt
+platform var foo: String
+
+// MODULE: m2-jvm(m1-common)
+// FILE: jvm.kt
+impl var foo: String = "JVM"
+
+// MODULE: m3-js(m1-common)
+// FILE: js.kt
+impl var foo: String = "JS"

compiler/testData/diagnostics/tests/multiplatform/topLevelProperty/simplePlatformVar.txt

@@ -0,0 +1,16 @@
+// -- Module: <m1-common> --
+package
+
+public var foo: kotlin.String
+
+
+// -- Module: <m2-jvm> --
+package
+
+public var foo: kotlin.String
+
+
+// -- Module: <m3-js> --
+package
+
+public var foo: kotlin.String