feat: qwik-city layout hierarchy updates

[adamdbradley]

• A layout can either be a filename _layout.tsx or a directory w/ an index _layout/index.tsx
• A layout (filename or directory name w/ index) can be given a name after a dash, such as _layout-foo.tsx
• If a page filename includes a @, then after the @ it's specifying which named layout to use. So about-us@foo.tsx would use the first _layout-foo.tsx in the hierarchy rather than _layout.tsx in the same directory.
• By default all layouts are nested and a page will crawl all the way up to the top of the routes directory to collect a hierarchy of nested layouts for the page.
• If at any point an applied layout filename ends with ! then it'll stop crawling up the directories and stop nesting at the current hierarchy.