Move SlashCommands and SlashCommands-test into subdirs (#31979)

* Move SlashCommands into slash-commands

* Move SlashCommands test prep into a function that can be re-used from multiple files

* Move slash command tests into separate files

* Fix super-linear regexes and test some more slash commands

* Move splitAtFirstSpace tests into a separate file

* Test for parseCommandString

* Make parseCommandString able to handle leading whitespace and tabs

* Implement parseCommandString using splitAtFirstSpace

* Extract emoticons slash commands into a separate file and share their code

test/unit-tests/slash-commands/parse-command-string-test.ts

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+import { parseCommandString } from "../../../src/slash-commands/SlashCommands";
+
+describe("parseCommandString", () => {
+    it("should be able to split arguments at the first whitespace", () => {
+        expect(parseCommandString("/a b")).toEqual({ cmd: "a", args: "b" });
+        expect(parseCommandString("/cmd And more stuff")).toEqual({ cmd: "cmd", args: "And more stuff" });
+        expect(parseCommandString("/cmd And more stuff")).toEqual({ cmd: "cmd", args: "And more stuff" });
+        expect(parseCommandString("/cmd And more\nstuff")).toEqual({ cmd: "cmd", args: "And more\nstuff" });
+        expect(parseCommandString("/cmd \t\n And more stuff")).toEqual({ cmd: "cmd", args: "And more stuff" });
+        expect(parseCommandString("/a")).toEqual({ cmd: "a" });
+        expect(parseCommandString("/cmd")).toEqual({ cmd: "cmd" });
+        expect(parseCommandString("/cmd    ")).toEqual({ cmd: "cmd" });
+        expect(parseCommandString("  /cmd    ")).toEqual({ cmd: "cmd" });
+    });
+});