Directory/Template Data Folders

[zachleat]

Surfaced by #647

Given the example on https://www.11ty.dev/docs/data-template-dir/:

• posts/subdir/my-first-blog-post.md

This would create additional data cascade folder checks for (using the standard data file suffix for folders in addition to files):

• posts/subdir/my-first-blog-post.11tydata/*.js
• posts/subdir/my-first-blog-post.11tydata/*.json
• posts/subdir/subdir.11tydata/*.js
• posts/subdir/subdir.11tydata/*.json
• posts/posts.11tydata/*.js
• posts/posts.11tydata/*.json

(including any custom data formats, as usual)

Files found in these folders would re-use the convention of a global data folder, where the file name would inform the variable name in the data cascade.