Custom context menu example (#1463)

* flutter create

* Copied in from 'contextual-menu-examples' repo

* Works again with the latest updates to the branch

* Clean up anywhere example

* Clean up other examples

* Add to CI

* Updated with release version of context menus, and added platform switcher

* Generated files

* Home icon on your original platform

* Remove web_dashboard from ci, not sure why that change was there...

* Add context_menu to beta channel, but commented out, for the future

* +x permissions on the master script, which I may have accidentally changed before?

* Actual bash comment

* dart format

* Natural default platform'

* A working test, for the email page

* Import order fix

* Test some pages

* More tests

* dart format

experimental/context_menus/android/build.gradle

@@ -0,0 +1,31 @@
+buildscript {
+    ext.kotlin_version = '1.7.10'
+    repositories {
+        google()
+        mavenCentral()
+    }
+
+    dependencies {
+        classpath 'com.android.tools.build:gradle:7.2.0'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+    }
+}
+
+allprojects {
+    repositories {
+        google()
+        mavenCentral()
+    }
+}
+
+rootProject.buildDir = '../build'
+subprojects {
+    project.buildDir = "${rootProject.buildDir}/${project.name}"
+}
+subprojects {
+    project.evaluationDependsOn(':app')
+}
+
+task clean(type: Delete) {
+    delete rootProject.buildDir
+}