Introduce inspection for redundant not-null extension receiver of inline

Related to KT-22303

idea/testData/inspections/redundantNotNullExtensionReceiverOfInline/inspectionData/expected.xml

@@ -0,0 +1,42 @@
+<problems>
+    <problem>
+        <file>test.kt</file>
+        <line>2</line>
+        <module>light_idea_test_case</module>
+        <entry_point TYPE="file" FQNAME="temp:///src/test.kt" />
+        <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Not-null extension receiver of inline function can be made nullable</problem_class>
+        <description>This type probably can be changed to nullable</description>
+    </problem>
+    <problem>
+        <file>test.kt</file>
+        <line>4</line>
+        <module>light_idea_test_case</module>
+        <entry_point TYPE="file" FQNAME="temp:///src/test.kt" />
+        <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Not-null extension receiver of inline function can be made nullable</problem_class>
+        <description>This type probably can be changed to nullable</description>
+    </problem>
+    <problem>
+        <file>test.kt</file>
+        <line>6</line>
+        <module>light_idea_test_case</module>
+        <entry_point TYPE="file" FQNAME="temp:///src/test.kt" />
+        <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Not-null extension receiver of inline function can be made nullable</problem_class>
+        <description>This type probably can be changed to nullable</description>
+    </problem>
+    <problem>
+        <file>test.kt</file>
+        <line>7</line>
+        <module>light_idea_test_case</module>
+        <entry_point TYPE="file" FQNAME="temp:///src/test.kt" />
+        <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Not-null extension receiver of inline function can be made nullable</problem_class>
+        <description>This type probably can be changed to nullable</description>
+    </problem>
+    <problem>
+        <file>test.kt</file>
+        <line>8</line>
+        <module>light_idea_test_case</module>
+        <entry_point TYPE="file" FQNAME="temp:///src/test.kt" />
+        <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Not-null extension receiver of inline function can be made nullable</problem_class>
+        <description>This type probably can be changed to nullable</description>
+    </problem>
+</problems>

idea/testData/inspections/redundantNotNullExtensionReceiverOfInline/inspectionData/inspections.test

@@ -0,0 +1 @@
+// INSPECTION_CLASS: org.jetbrains.kotlin.idea.inspections.RedundantNotNullExtensionReceiverOfInlineInspection

idea/testData/inspections/redundantNotNullExtensionReceiverOfInline/test.kt

@@ -0,0 +1,51 @@
+// Typical true positive
+inline fun String.foo() = foo(this)
+fun String.notInlineFoo() = foo(this)
+inline fun String.eq(other: Any?) = this == other
+// Other positives
+inline fun String.fooo1() = fooo()
+inline fun String.fooo2() = this.fooo()
+inline fun String.fooo3() = this?.foo()
+
+// Just functions
+fun foo(s: String?) {}
+fun String?.fooo() {}
+fun bar(s: String) {}
+fun String.baz() = this
+
+inline fun String.bar() = bar(this) // No problem
+inline fun String.bazz() = baz() // No problem
+inline fun String.bazzx() = baz().baz() // No problem
+inline fun String.bazzz() = this.baz() // No problem
+
+interface My {
+    inline fun String.bar() // No problem (no body)
+}
+
+inline fun String.myLength() = length // No problem (this.length)
+
+// No problem (this.size)
+inline fun <reified T> List<T>.count() {
+    return size
+}
+
+// No problem (in this)
+inline fun <reified T> List<T>.foo() {
+    for (element in this) {}
+}
+
+// No problem (cast)
+inline fun String.cast(): Any = this as Any
+
+class Some {
+    companion object {}
+}
+
+fun Some.Companion.foo() {} // No problem (on companion)
+inline fun Int.baz(x: Int) = this + x // No problem
+inline fun Int.bar(x: Int) = x - this // No problem
+
+inline fun Int.unary() = -this // No problem
+inline fun String.indexed(arg: Int) = this[arg] // No problem
+
+