framework: Add new USES 'magick' for graphics/ImageMagick*

A new USES has been added to depend on ImageMagick.

USES=magick

adds a LIB_DEPENDS on graphics/ImageMagick${IMAGEMAGICK_DEFAULT}.

If a specific version is required, use for example

USES=magick:6 resp. USES=magick:7

If only a build, run or test is required, use for example

USES=magick:build resp. USES=magick:6,build,test

If a dependency on the nox11 flavor is required, use for example

USES=magick:nox11 resp. USES=magick:7,nox11,run,test

See magick.mk for more details on the available flags.

The tree has been completely converted to make use of this.

Approved by: bapt
Differential Revision: https://reviews.freebsd.org/D32754