vfmt: keep selective imported names used for generic calls

vlib/v/fmt/fmt.v

@@ -1694,6 +1694,7 @@ fn (mut f Fmt) write_generic_call_if_require(node ast.CallExpr) {
 				name = 'JS.' + name
 			}
 			f.write(name)
+			f.mark_import_as_used(name)
 			if i != node.concrete_types.len - 1 {
 				f.write(', ')
 			}

vlib/v/fmt/tests/import_selective_keep.vv

@@ -1,12 +1,16 @@
 import math.complex { Complex }
 import gg { MouseButton }
 import time { Duration }
+import modtest { Test }
 
 fn keep_imported_enum_map_key() {
 	bm := map[MouseButton]string{}
 }
 
+fn generic<T>() {}
+
 fn main() {
 	_ := Duration(10) // keep cast type
 	assert *(&f64(&byte(&num) + __offsetof(Complex, re))) == 1.0
+	generic<Test>()
 }