docs(require-event-prefix): added rule docs

docs/rules/require-event-prefix.md

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+---
+pageClass: 'rule-details'
+sidebarDepth: 0
+title: 'svelte/require-event-prefix'
+description: 'require component event names to start with "on"'
+---
+
+# svelte/require-event-prefix
+
+> require component event names to start with "on"
+
+- :exclamation: <badge text="This rule has not been released yet." vertical="middle" type="error"> **_This rule has not been released yet._** </badge>
+
+## :book: Rule Details
+
+Starting with Svelte 5, component events are just component props that are functions and so can be called like any function. Events for HTML elements all have their name begin with "on" (e.g. `onclick`). This rule enforces that all component events (i.e. function props) also begin with "on".
+
+<!--eslint-skip-->
+
+```svelte
+<script lang="ts">
+  /* eslint svelte/require-event-prefix: "error" */
+
+  /* ✓ GOOD */
+
+  interface Props {
+    regularProp: string;
+    onclick(): void;
+  }
+
+  let { regularProp, onclick }: Props = $props();
+</script>
+```
+
+```svelte
+<script lang="ts">
+  /* eslint svelte/require-event-prefix: "error" */
+
+  /* ✗ BAD */
+
+  interface Props {
+    click(): void;
+  }
+
+  let { click }: Props = $props();
+</script>
+```
+
+## :wrench: Options
+
+```json
+{
+  "svelte/require-event-prefix": [
+    "error",
+    {
+      "checkAsyncFunctions": false
+    }
+  ]
+}
+```
+
+- `checkAsyncFunctions` ... Whether to also report asychronous function properties. Default `false`.
+
+## :books: Further Reading
+
+- [Svelte docs on events in version 5](https://svelte.dev/docs/svelte/v5-migration-guide#Event-changes)
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/sveltejs/eslint-plugin-svelte/blob/main/packages/eslint-plugin-svelte/src/rules/require-event-prefix.ts)
+- [Test source](https://github.com/sveltejs/eslint-plugin-svelte/blob/main/packages/eslint-plugin-svelte/tests/src/rules/require-event-prefix.ts)