KT-15286: Provide object member extensions in the completion

- Add extensions only when completion of static members is enabled (double ctrl + space and nonempty prefix)
- Add full import for callables with receiver in `LookupElement.decorateAsStaticMember`

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/CompanionObjectInSameFileExplicitReceiver.kt

@@ -0,0 +1,12 @@
+class T {
+    companion object {
+        fun T.foo() {}
+    }
+}
+
+fun usage(t: T) {
+    t.f<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/CompanionObjectInSameFileExplicitReceiver.kt.after

@@ -0,0 +1,14 @@
+import T.Companion.foo
+
+class T {
+    companion object {
+        fun T.foo() {}
+    }
+}
+
+fun usage(t: T) {
+    t.foo()<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/CompanionObjectInSameFileImplicitReceiver.kt

@@ -0,0 +1,12 @@
+class T {
+    companion object {
+        fun T.foo() {}
+    }
+}
+
+fun T.usage() {
+    f<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/CompanionObjectInSameFileImplicitReceiver.kt.after

@@ -0,0 +1,14 @@
+import T.Companion.foo
+
+class T {
+    companion object {
+        fun T.foo() {}
+    }
+}
+
+fun T.usage() {
+    foo()<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/NestedCompanionObjectInSameFileExplicitReceiver.kt

@@ -0,0 +1,16 @@
+class T
+
+class A {
+    class B {
+        companion object {
+            fun T.foo() {}
+        }
+    }
+}
+
+fun usage(t: T) {
+    t.f<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/NestedCompanionObjectInSameFileExplicitReceiver.kt.after

@@ -0,0 +1,18 @@
+import A.B.Companion.foo
+
+class T
+
+class A {
+    class B {
+        companion object {
+            fun T.foo() {}
+        }
+    }
+}
+
+fun usage(t: T) {
+    t.foo()<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/NestedCompanionObjectInSameFileImplicitReceiver.kt

@@ -0,0 +1,16 @@
+class T
+
+class A {
+    class B {
+        companion object {
+            fun T.foo() {}
+        }
+    }
+}
+
+fun T.usage() {
+    f<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/NestedCompanionObjectInSameFileImplicitReceiver.kt.after

@@ -0,0 +1,18 @@
+import A.B.Companion.foo
+
+class T
+
+class A {
+    class B {
+        companion object {
+            fun T.foo() {}
+        }
+    }
+}
+
+fun T.usage() {
+    foo()<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/NestedObjectInSameFileExplicitReceiver.kt

@@ -0,0 +1,14 @@
+class T
+
+object TopLevel {
+    object Nested {
+        fun T.foo() {}
+    }
+}
+
+fun usage(t: T) {
+    t.f<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/NestedObjectInSameFileExplicitReceiver.kt.after

@@ -0,0 +1,16 @@
+import TopLevel.Nested.foo
+
+class T
+
+object TopLevel {
+    object Nested {
+        fun T.foo() {}
+    }
+}
+
+fun usage(t: T) {
+    t.foo()<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/NestedObjectInSameFileImplicitReceiver.kt

@@ -0,0 +1,14 @@
+class T
+
+object TopLevel {
+    object Nested {
+        fun T.foo() {}
+    }
+}
+
+fun T.usage() {
+    f<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/NestedObjectInSameFileImplicitReceiver.kt.after

@@ -0,0 +1,16 @@
+import TopLevel.Nested.foo
+
+class T
+
+object TopLevel {
+    object Nested {
+        fun T.foo() {}
+    }
+}
+
+fun T.usage() {
+    foo()<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/ObjectInSameFileExplicitReceiver.kt

@@ -0,0 +1,12 @@
+class T
+
+object Extensions {
+    fun T.foo() {}
+}
+
+fun usage(t: T) {
+    t.f<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/ObjectInSameFileExplicitReceiver.kt.after

@@ -0,0 +1,14 @@
+import Extensions.foo
+
+class T
+
+object Extensions {
+    fun T.foo() {}
+}
+
+fun usage(t: T) {
+    t.foo()<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/ObjectInSameFileImplicitReceiver.kt

@@ -0,0 +1,12 @@
+class T
+
+object Extensions {
+    fun T.foo() {}
+}
+
+fun T.usage() {
+    f<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo

idea/idea-completion/testData/handlers/basic/extensionMethodInObject/ObjectInSameFileImplicitReceiver.kt.after

@@ -0,0 +1,14 @@
+import Extensions.foo
+
+class T
+
+object Extensions {
+    fun T.foo() {}
+}
+
+fun T.usage() {
+    foo()<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ELEMENT: foo