filters/color_matrix.rs: Separate functions for each matrix type
filters/color_matrix.rs: Separate functions for each matrix type

First set the initial value of the matrix that corresponds to the
operation_type, and then try to parse the final value.  If the value
is invalid, the initial value remains unchanged - per the spec.

Part-of: <https://gitlab.gnome.org/GNOME/librsvg/-/merge_requests/763>

GNOME/librsvg,GNOME/librsvg,GNOME/librsvg,GNOME/librsvg