Use generics for DepSets

Use Go's generics for DepSets so they don't require a type-specific
wrapper and reflection.

Test: depsets_test.go
Change-Id: I22ba0b7d680d37d2cd05230b0f560d166c4dd20b
diff --git a/go.mod b/go.mod
index 4a511c5..0a11bd2 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module android/soong
 
-go 1.19
+go 1.20
 
 require (
 	github.com/google/blueprint v0.0.0