Vue 3: Fix undefined relativeIncludesDir and relativeLayoutsDir properties

[arcxyz]

I reach the following error while testing the Vue 3 version on a project that is currently working with Vue 2 templates:

[11ty] Problem writing Eleventy templates: (more in DEBUG output)
[11ty] > The "path" argument must be of type string. Received undefined

`TypeError` was thrown:
[11ty]     TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received undefined
        at new NodeError (node:internal/errors:371:5)
        at validateString (node:internal/validators:120:11)
        at Object.join (node:path:1172:7)
        at EleventyVue.findFiles ([...]/node_modules/@11ty/eleventy-plugin-vue/EleventyVue.js:246:35)
        at Object.init ([...]/node_modules/@11ty/eleventy-plugin-vue/.eleventy.js:135:39)
        at CustomEngine._runningInit ([...]/node_modules/@11ty/eleventy/src/Engines/Custom.js:57:11)
        at CustomEngine.getExtraDataFromFile ([...]/node_modules/@11ty/eleventy/src/Engines/Custom.js:74:16)
        at Template.getFrontMatterData ([...]/node_modules/@11ty/eleventy/src/TemplateContent.js:209:39)
        at processTicksAndRejections (node:internal/process/task_queues:96:5)
        at async Template.getData ([...]/node_modules/@11ty/eleventy/src/Template.js:404:29)
[11ty] Wrote 0 files in 0.01 seconds (v1.0.0)

The findFiles method is trying to read some undefined properties:

https://github.com/11ty/eleventy-plugin-vue/blob/master/EleventyVue.js#L246
https://github.com/11ty/eleventy-plugin-vue/blob/master/EleventyVue.js#L254