Move API factories to the common package

We don't actually use this functionality in other projects (e.g.
emulators). In fact the method to add new APIs only exists in the mod
itself!

We still need some mechanism to remove mounts when the computer is
shutdown. We add a new ApiLifecycle interface (with startup and
shutdown hooks), and use those in the ComputerSystem impl.

projects/common-api/src/main/java/dan200/computercraft/api/lua/IComputerSystem.java

@@ -0,0 +1,25 @@
+// SPDX-FileCopyrightText: 2017 The CC: Tweaked Developers
+//
+// SPDX-License-Identifier: MPL-2.0
+
+package dan200.computercraft.api.lua;
+
+import dan200.computercraft.api.peripheral.IComputerAccess;
+import org.jetbrains.annotations.ApiStatus;
+
+import javax.annotation.Nullable;
+
+/**
+ * An interface passed to {@link ILuaAPIFactory} in order to provide additional information
+ * about a computer.
+ */
+@ApiStatus.NonExtendable
+public interface IComputerSystem extends IComputerAccess {
+    /**
+     * Get the label for this computer.
+     *
+     * @return This computer's label, or {@code null} if it is not set.
+     */
+    @Nullable
+    String getLabel();
+}

projects/common-api/src/main/java/dan200/computercraft/api/lua/ILuaAPIFactory.java

@@ -0,0 +1,27 @@
+// SPDX-FileCopyrightText: 2017 The CC: Tweaked Developers
+//
+// SPDX-License-Identifier: MPL-2.0
+
+package dan200.computercraft.api.lua;
+
+import dan200.computercraft.api.ComputerCraftAPI;
+
+import javax.annotation.Nullable;
+
+/**
+ * Construct an {@link ILuaAPI} for a computer.
+ *
+ * @see ILuaAPI
+ * @see ComputerCraftAPI#registerAPIFactory(ILuaAPIFactory)
+ */
+@FunctionalInterface
+public interface ILuaAPIFactory {
+    /**
+     * Create a new API instance for a given computer.
+     *
+     * @param computer The computer this API is for.
+     * @return The created API, or {@code null} if one should not be injected.
+     */
+    @Nullable
+    ILuaAPI create(IComputerSystem computer);
+}