runtime: add cap and len support for chans

testdata/channel.go

@@ -9,7 +9,11 @@ import (
 var wg sync.WaitGroup
 
 func main() {
-	ch := make(chan int)
+	ch := make(chan int, 2)
+	ch <- 1
+	println("len, cap of channel:", len(ch), cap(ch), ch == nil)
+
+	ch = make(chan int)
 	println("len, cap of channel:", len(ch), cap(ch), ch == nil)
 
 	wg.Add(1)

testdata/channel.txt

@@ -1,3 +1,4 @@
+len, cap of channel: 1 2 false
 len, cap of channel: 0 0 false
 recv from open channel: 1 true
 received num: 2