[FIR] Put new contract syntax under feauture flag

^KT-55171 Fixed

compiler/fir/analysis-tests/testData/resolve/contracts/contractFromOtherModule.kt

@@ -1,3 +1,4 @@
+// LANGUAGE: +ContractSyntaxV2
 // SKIP_JAVAC
 // This directive is needed to skip this test in LazyBodyIsNotTouchedTilContractsPhaseTestGenerated,
 //  because it fails to parse module structure of multimodule test

compiler/fir/analysis-tests/testData/resolve/contracts/contractFromOtherModule_samePackage.kt

@@ -1,3 +1,4 @@
+// LANGUAGE: +ContractSyntaxV2
 // SKIP_JAVAC
 // This directive is needed to skip this test in LazyBodyIsNotTouchedTilContractsPhaseTestGenerated,
 //  because it fails to parse module structure of multimodule test

compiler/fir/analysis-tests/testData/resolve/contracts/disabledFeature.fir.txt

@@ -0,0 +1,34 @@
+FILE: disabledFeature.kt
+    public final inline fun <reified T> requreIsInstance(value: R|kotlin/Any|): R|kotlin/Unit|
+        [R|Contract description]
+         <
+            Returns(WILDCARD) -> value is T
+        >
+     {
+        when () {
+            (R|<local>/value| !is R|T|) ->  {
+                throw R|java/lang/IllegalArgumentException.IllegalArgumentException|()
+            }
+        }
+
+    }
+    public final val R|kotlin/Any?|.myLength: R|kotlin/Int?|
+        public get(): R|kotlin/Int?|
+            [R|Contract description]
+             <
+            >
+         {
+            ^ (this@R|/myLength| as? R|kotlin/String|)?.{ $subj$.R|kotlin/String.length| }
+        }
+    public final fun test_1(x: R|kotlin/Any|): R|kotlin/Unit| {
+        R|/requreIsInstance|<R|kotlin/String|>(R|<local>/x|)
+        R|<local>/x|.R|kotlin/String.length|
+    }
+    public final fun test_2(x: R|kotlin/Any|): R|kotlin/Unit| {
+        when () {
+            !=(R|<local>/x|.R|/myLength|, Null(null)) ->  {
+                R|<local>/x|.<Unresolved name: length>#
+            }
+        }
+
+    }

compiler/fir/analysis-tests/testData/resolve/contracts/disabledFeature.kt

@@ -0,0 +1,26 @@
+// LANGUAGE: -ContractSyntaxV2
+// WITH_STDLIB
+
+import kotlin.contracts.*
+
+inline fun <reified T> requreIsInstance(value: Any) contract <!UNSUPPORTED_FEATURE!>[
+    returns() implies (value is T)
+]<!> {
+    if (value !is T) throw IllegalArgumentException()
+}
+
+val Any?.myLength: Int?
+    get() contract <!UNSUPPORTED_FEATURE!>[
+        <!ERROR_IN_CONTRACT_DESCRIPTION!>returnsNotNull() implies (this@length is String)<!>
+    ]<!> = (this as? String)?.length
+
+fun test_1(x: Any) {
+    requreIsInstance<String>(x)
+    x.length
+}
+
+fun test_2(x: Any) {
+    if (x.myLength != null) {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+}

compiler/fir/analysis-tests/testData/resolve/contracts/genericContract.kt

@@ -1,3 +1,4 @@
+// LANGUAGE: +ContractSyntaxV2
 // WITH_STDLIB
 
 import kotlin.contracts.*

compiler/fir/analysis-tests/testData/resolveWithStdlib/contracts/fromSource/good/variousContracts/newSyntax/functionsWithContract.kt

@@ -1,3 +1,4 @@
+// LANGUAGE: +ContractSyntaxV2
 import kotlin.contracts.*
 
 fun test1(arg: Any?) contract [
@@ -19,4 +20,4 @@ fun test3(arg: Any?): Boolean contract [
 ] {
     require(arg != null)
     return true
-}
+}