Add includes field to Library Manager index and search scope

[per1234]

Often when searching for a dependency of someone's code the only information we have is the #include directive for the missing file and so that filename is the logical term to use in a Library Manager search query. That filename is not necessarily found in the library.properties fields currently used by the Library Manager search.

Adding the library.properties includes field to the Library Manager search scope will increase the chances of finding a library by searching for the primary header filename.

This will require adding that field to the Library Manager index JSON file.

[cmaglie]

The field is now available on the library_index.json as providesIncludes. I've extended the search on the Library Manager too.