Add support for slash commands (under Feature Flag) (#6482)

* Add support for slash commands

* Update screenshots

* Rename module `slash` to `slashcommands`

* Rename `SlashCommand` to `SlashCommandService`

* Introduce MsgType in order to send text message with a different msgtype value.

* Format file and add parameter names, add default values and cleanup

* Add isSupported parameter to filter out unsupported yet commands.

* Slash commands: disable suggestions if the feature is disabled.

* Fix sending shrug command.

* Add missing test on SuggestionsProcessor

* Add tests on MessageComposerPresenter about slash command.

* Fix import ordering

* Add missing tests on CommandExecutor

* Add missing tests in MarkdownTextEditorStateTest

* Slash commands: Improve code when sending message with prefix.

* Slash commands: Add support for /unflip

---------

Co-authored-by: ElementBot <android@element.io>

libraries/slashcommands/impl/build.gradle.kts

@@ -0,0 +1,35 @@
+import extension.setupDependencyInjection
+import extension.testCommonDependencies
+
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+plugins {
+    id("io.element.android-library")
+}
+
+android {
+    namespace = "io.element.android.libraries.slashcommands.impl"
+}
+
+setupDependencyInjection()
+
+dependencies {
+    implementation(projects.libraries.androidutils)
+    implementation(projects.libraries.preferences.api)
+    implementation(projects.libraries.core)
+    implementation(projects.libraries.matrix.api)
+    api(projects.libraries.slashcommands.api)
+    implementation(projects.libraries.di)
+    implementation(projects.libraries.featureflag.api)
+    implementation(projects.services.toolbox.api)
+
+    testCommonDependencies(libs)
+    testImplementation(projects.libraries.featureflag.test)
+    testImplementation(projects.libraries.preferences.test)
+    testImplementation(projects.libraries.matrix.test)
+    testImplementation(projects.services.toolbox.test)
+}