Set view paths on each page, taking multi-site into consideration

[davebarrau]

Fixes #127.

Currently if you have two sites in a multi-site setup, say, for example, default and test.

Using php please ssg:generate, if you attempt to generate a page that is part of the test site, the view path resources/views/test/ will never be added to the list of view paths to find files in, so you cannot override the layouts/partials/other files.

Because statamic/cms has the AddViewPaths HTTP middleware, it works when visiting the site, just not when using the static site generator. Ideally the logic currently in the AddViewPaths middleware would be split out so SSG can use the parts of it it needs, but this should hopefully be a sufficient improvement for now.

Co-authored by: @michaelr0

[what-the-diff[bot]]

• Added a backupViewPaths() method to store the current view paths.
• Added a restoreViewPaths() method to set the stored view paths back after generating static files for each site.
• Updated createContentFiles(), updateCurrentSite($site), and shouldSetCarbonFormat($page) methods by adding calls to setViewPaths(). This is needed because we are changing the views directory when switching between sites, so it needs to be reset before rendering pages from other sites (e.g., pagination links).

[davebarrau]

@jasonvarga When you get a chance, can you please review this? 🙇

[jasonvarga]

Closing this as it's been sitting a while, and needs changes applied in order to work properly. If you'd like to make the requested changes we can reopen it. Thanks!