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}"]
+      }
+    }
+  }
+}