Use ECMGenerateExportHeader to manage deprecated API better

Summary:
Allows

• projects linking to KIO to hide deprecated API up to a given version or silence deprecation warnings after a given version, using
  • -DKIOCORE_DISABLE_DEPRECATED_BEFORE_AND_AT
  • -DKIOCORE_NO_DEPRECATED
  • -DKIOCORE_DEPRECATED_WARNINGS_SINCE
  • -DKIOCORE_NO_DEPRECATED_WARNINGS
  • -DKIOFILEWIDGETS_DISABLE_DEPRECATED_BEFORE_AND_AT
  • -DKIOFILEWIDGETS_NO_DEPRECATED
  • -DKIOFILEWIDGETS_DEPRECATED_WARNINGS_SINCE
  • -DKIOFILEWIDGETS_NO_DEPRECATED_WARNINGS
  • -DKIOWIDGETS_DISABLE_DEPRECATED_BEFORE_AND_AT
  • -DKIOWIDGETS_NO_DEPRECATED
  • -DKIOWIDGETS_DEPRECATED_WARNINGS_SINCE
  • -DKIOWIDGETS_NO_DEPRECATED_WARNINGS
    
    or (once enabled when all KF modules are done)
  • -DKF_DISABLE_DEPRECATED_BEFORE_AND_AT
  • -DKF_NO_DEPRECATED
  • -DKF_DEPRECATED_WARNINGS_SINCE
  • -DKF_NO_DEPRECATED_WARNINGS

No support for "EXCLUDE_DEPRECATED_BEFORE_AND_AT" yet, some
undeprecated API is implemented by deprecated API still, at least for
some deprecation versions. This needs separate work.

Reviewers: Frameworks, dfaure

Reviewed By: dfaure

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D24684