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/basic/common/extensionMethodInObject/CompanionObjectExplicitReceiver.kt

@@ -0,0 +1,16 @@
+class T
+
+class A {
+    companion object {
+        fun T.fooExtension() {}
+        val T.fooProperty get() = 10
+    }
+}
+
+fun usage(t: T) {
+    t.foo<caret>
+}
+
+// INVOCATION_COUNT: 2
+// EXIST: { lookupString: "fooExtension", itemText: "fooExtension" }
+// EXIST: { lookupString: "fooProperty", itemText: "fooProperty" }

idea/idea-completion/testData/basic/common/extensionMethodInObject/CompanionObjectImplicitReceiver.kt

@@ -0,0 +1,16 @@
+class T
+
+class A {
+    companion object {
+        fun T.fooExtension() {}
+        val T.fooProperty get() = 10
+    }
+}
+
+fun T.usage() {
+    foo<caret>
+}
+
+// INVOCATION_COUNT: 2
+// EXIST: { lookupString: "fooExtension", itemText: "fooExtension" }
+// EXIST: { lookupString: "fooProperty", itemText: "fooProperty" }

idea/idea-completion/testData/basic/common/extensionMethodInObject/CorrectTypeExplicitReceiver.kt

@@ -0,0 +1,35 @@
+interface T
+interface B: T
+interface C: T
+
+object A {
+    fun Any.fooForAny() {}
+
+    fun T.fooForT() {}
+    fun B.fooForB() {}
+    fun C.fooForC() {}
+
+    fun <TT> TT.fooForAnyGeneric() {}
+    fun <TT: T> TT.fooForTGeneric() {}
+    fun <TT: B> TT.fooForBGeneric() {}
+    fun <TT: C> TT.fooForCGeneric() {}
+
+    fun fooNoReceiver() {}
+}
+
+fun usage(b: B) {
+    b.foo<caret>
+}
+
+// INVOCATION_COUNT: 2
+// EXIST: { lookupString: "fooForAny", itemText: "fooForAny" }
+
+// EXIST: { lookupString: "fooForT", itemText: "fooForT" }
+// EXIST: { lookupString: "fooForB", itemText: "fooForB" }
+
+// EXIST: { lookupString: "fooForTGeneric", itemText: "fooForTGeneric" }
+// EXIST: { lookupString: "fooForBGeneric", itemText: "fooForBGeneric" }
+
+// ABSENT: fooForC
+// ABSENT: fooForCGeneric
+// ABSENT: fooNoReceiver

idea/idea-completion/testData/basic/common/extensionMethodInObject/CorrectTypeImplicitReceiver.kt

@@ -0,0 +1,36 @@
+interface T
+interface B: T
+interface C: T
+
+object A {
+    fun Any.fooForAny() {}
+
+    fun T.fooForT() {}
+    fun B.fooForB() {}
+    fun C.fooForC() {}
+
+    fun <TT> TT.fooForAnyGeneric() {}
+    fun <TT: T> TT.fooForTGeneric() {}
+    fun <TT: B> TT.fooForBGeneric() {}
+    fun <TT: C> TT.fooForCGeneric() {}
+
+    fun fooNoReceiver() {}
+}
+
+fun B.usage() {
+    foo<caret>
+}
+
+// INVOCATION_COUNT: 2
+// EXIST: { lookupString: "fooForAny", itemText: "fooForAny" }
+
+// EXIST: { lookupString: "fooForT", itemText: "fooForT" }
+// EXIST: { lookupString: "fooForB", itemText: "fooForB" }
+
+// EXIST: { lookupString: "fooForTGeneric", itemText: "fooForTGeneric" }
+// EXIST: { lookupString: "fooForBGeneric", itemText: "fooForBGeneric" }
+
+// EXIST: fooNoReceiver
+
+// ABSENT: fooForC
+// ABSENT: fooForCGeneric

idea/idea-completion/testData/basic/common/extensionMethodInObject/MultipleImplicitReceivers.kt

@@ -0,0 +1,24 @@
+class T
+
+object O {
+    fun A.fooForA() {}
+    fun A.B.fooForB() {}
+    fun A.B.C.fooForC() {}
+    fun T.fooForT() {}
+}
+
+class A {
+    inner class B {
+        fun T.usage() {
+            foo<caret>
+        }
+
+        inner class C {}
+    }
+}
+
+// INVOCATION_COUNT: 2
+// EXIST: { lookupString: "fooForA", itemText: "fooForA" }
+// EXIST: { lookupString: "fooForB", itemText: "fooForB" }
+// EXIST: { lookupString: "fooForT", itemText: "fooForT" }
+// ABSENT: fooForC

idea/idea-completion/testData/basic/common/extensionMethodInObject/ObjectExplicitReceiver.kt

@@ -0,0 +1,14 @@
+class T
+
+object A {
+    fun T.fooExtension() {}
+    val T.fooProperty get() = 10
+}
+
+fun usage(t: T) {
+    t.foo<caret>
+}
+
+// INVOCATION_COUNT: 2
+// EXIST: { lookupString: "fooExtension", itemText: "fooExtension" }
+// EXIST: { lookupString: "fooProperty", itemText: "fooProperty" }

idea/idea-completion/testData/basic/common/extensionMethodInObject/ObjectImplicitReceiver.kt

@@ -0,0 +1,14 @@
+class T
+
+object A {
+    fun T.fooExtension() {}
+    val T.fooProperty get() = 10
+}
+
+fun T.usage() {
+    foo<caret>
+}
+
+// INVOCATION_COUNT: 2
+// EXIST: { lookupString: "fooExtension", itemText: "fooExtension" }
+// EXIST: { lookupString: "fooProperty", itemText: "fooProperty" }

idea/idea-completion/testData/basic/common/extensionMethodInObject/OverridenExtensionsInObject.kt

@@ -0,0 +1,19 @@
+class T
+
+interface Foo {
+    fun T.fooExtension()
+    val T.fooProperty: Int
+}
+
+object A : Foo {
+    override fun T.fooExtension() {}
+    override val T.fooProperty get() = 10
+}
+
+fun T.usage() {
+    foo<caret>
+}
+
+// INVOCATION_COUNT: 2
+// EXIST: { lookupString: "fooExtension", itemText: "fooExtension" }
+// EXIST: { lookupString: "fooProperty", itemText: "fooProperty" }