wined3d: Add read_from_framebuffer_texture which combines code from read_from_framebuffer (drawpixels) and LoadLocation.

This makes the code easier to read and the pieces borrowed from
read_from_framebuffer are more correct than the code in LoadLocation.

There is no need to use cmd_insertLinkNoUI when we have the code to do 
most of the action anyway. Make use of the handy 
InsertLinkAroundSelection to insert the "a" element when not inserting 
at the caret and don't create a text node in this case because it is 
redundant.

rsaenh: Merge the encrypting and decrypting states, as encrypting and decrypting are allowed with the same key.