Add regression tests for lua support

Change Dockerfile to install lua, luajit and love and also to install
nodejs 12 needed to build the lua debug adapter. Create the
love-headless test in support/test/lua to test love without an x server.

support/test/lua/love-headless/.vimspector.json

@@ -0,0 +1,17 @@
+{
+  "$schema": "https://puremourning.github.io/vimspector/schema/vimspector.schema.json#",
+  "configurations": {
+    "love": {
+      "adapter": "lua-local",
+      "configuration": {
+        "request": "launch",
+        "type": "lua-local",
+        "cwd": "${workspaceFolder}",
+        "program": {
+          "command": "love"
+        },
+        "args": ["${workspaceFolder}"]
+      }
+    }
+  }
+}

support/test/lua/love-headless/conf.lua

@@ -0,0 +1,12 @@
+function love.conf(t)
+    t.modules.audio = false
+    t.modules.font = false
+    t.modules.graphics = false
+    t.modules.image = false
+    t.modules.mouse = false
+    t.modules.physics = false
+    t.modules.sound = false
+    t.modules.touch = false
+    t.modules.video = false
+    t.modules.window = false
+end

support/test/lua/love-headless/main.lua

@@ -0,0 +1,10 @@
+if pcall(require, 'lldebugger') then
+  require('lldebugger').start()
+end
+
+local time = 0
+
+function love.update(dt)
+  time = time + dt
+  love.event.quit()
+end