Color matrix defines for filters and identity (#80320)

This PR converts the procs `color_matrix_identity`,
`color_matrix_lightness` and `color_matrix_contrast` into
defines/macros. Also adds in defines for common color matrix filters.

I don't like how `color_matrix_identity` is a one-line proc with no arg.
Also these help people identify the sort of color matrix filter is being
used.

code/modules/client/client_colour.dm

@@ -191,7 +191,7 @@
 	colour = list(/*R*/ 0,0,0,0, /*G*/ 0,175,0,0, /*B*/ 0,0,0,0, /*A*/ 0,0,0,1, /*C*/0,-130,0,0) // Matrix colors
 
 /datum/client_colour/monochrome
-	colour = list(rgb(77,77,77), rgb(150,150,150), rgb(28,28,28), rgb(0,0,0))
+	colour = COLOR_MATRIX_GRAYSCALE
 	priority = PRIORITY_HIGH //we can't see colors anyway!
 	override = TRUE
 	fade_in = 20