Move `librz/cons/grep.c` (`~`) command from the RzCons to the RzCore

[XVilka]

It has nothing to do with the RzCons and belongs along with other commands handling, in RzCore. It also should be better integrated with the rzshell.

• librz/cons/grep.c
• librz/include/rz_cons.h
• librz/core/cmd.c

See also：

• https://github.com/rizinorg/rizin/issues/276
• https://github.com/rizinorg/rizin/issues/985
• https://github.com/rizinorg/rizin/issues/1342

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