Support suppression on expressions

compiler/testData/diagnostics/tests/suppress/allWarnings/suppressWarningsOnExpression.kt

@@ -0,0 +1,4 @@
+fun foo() {
+    [suppress("warnings")]
+    ("": String??)
+}

compiler/testData/diagnostics/tests/suppress/manyWarnings/onExpression.kt

@@ -0,0 +1,4 @@
+fun foo(): Any? {
+    [suppress("REDUNDANT_NULLABLE", "UNNECESSARY_NOT_NULL_ASSERTION")]
+    return ""!! <!USELESS_CAST_STATIC_ASSERT_IS_FINE!>as<!> String??
+}

compiler/testData/diagnostics/tests/suppress/oneWarning/onExpression.kt

@@ -0,0 +1,4 @@
+fun foo(): Any? {
+    [suppress("REDUNDANT_NULLABLE")]
+    return null <!USELESS_CAST!>as<!> Nothing??
+}