generics: implement method generics (fix #7638) (#7732)

vlib/v/tests/generics_method_test.v

@@ -0,0 +1,21 @@
+struct Point {
+mut:
+	x int
+	y int
+}
+
+fn (mut p Point) translate<T>(x T, y T) {
+	p.x += x
+	p.y += y
+}
+
+fn test_generic_method() {
+	mut pot := Point{}
+	pot.translate<int>(1, 3)
+	pot.translate(1, 3)
+	println(pot)
+	assert pot == Point{
+		x: 2
+		y: 6
+	}
+}