build: enhance resolve_spec_data to support default variables

[akritkbehera]

Pass defaults-profile variables to recipes, better undefined-variable errors, and file includes

• Variables defined in defaults are now available for all package recipes.
• Undefined %(var)s now errors with the variable name instead of a bare KeyError
• %(##INCLUDE:configdir/file)s expands a file inline during parsing.
  Reason: If we simple source another file it has an variable that isn't expanded.
  As this is done before hashing changes to the file will lead to rebuild.

[pbuncic]

What issues are we trying to solve by adding INCLUDE processing and additional variables?