Add deleteContext to Context API

Solves #6255

src/runtime/internal/lifecycle.ts

@@ -55,7 +55,11 @@ export function getContext<T>(key): T {
 }
 
 export function hasContext(key): boolean {
-	return get_current_component().$$.context.has(key);	
+	return get_current_component().$$.context.has(key);
+}
+
+export function deleteContext(key): boolean {
+	return get_current_component().$$.context.delete(key);
 }
 
 // TODO figure out if we still want to support

test/runtime/samples/context-api-d/Delete.svelte

@@ -0,0 +1,8 @@
+<script>
+	import { deleteContext } from 'svelte';
+
+	const deleted = deleteContext('test');
+</script>
+
+<div>{deleted}</div>
+<slot />

test/runtime/samples/context-api-d/Leaf.svelte

@@ -0,0 +1,8 @@
+<script>
+	import { hasContext } from 'svelte';
+
+	const has = hasContext('test');
+</script>
+
+<div>{has}</div>
+<slot />

test/runtime/samples/context-api-d/Nested.svelte

@@ -0,0 +1,7 @@
+<script>
+	import { setContext } from 'svelte';
+
+	setContext('test', true);
+</script>
+
+<slot></slot>

test/runtime/samples/context-api-d/_config.js

@@ -0,0 +1,7 @@
+export default {
+	html: `
+		<div>true</div>
+		<div>false</div>
+		<div>false</div>
+	`
+};

test/runtime/samples/context-api-d/main.svelte

@@ -0,0 +1,13 @@
+<script>
+  import Nested from "./Nested.svelte";
+  import Delete from "./Delete.svelte";
+  import Leaf from "./Leaf.svelte";
+</script>
+
+<Nested>
+	<Delete>
+		<Leaf>
+			<Delete />
+		</Leaf>
+	</Delete>
+</Nested>