json: move _test.v files to vlib/json/tests/ (#22731)

vlib/json/json_encode_embed_test.v

@@ -1,27 +0,0 @@
-import json
-
-struct Json2 {
-	inner []f64
-}
-
-struct Json {
-	Json2
-	test f64
-}
-
-fn test_main() {
-	str := '{"inner":[1,2,3,4,5],"test":1.2}'
-	data := json.decode(Json, str) or {
-		eprintln('Failed to decode json, error: ${err}')
-		return
-	}
-	println(data)
-	assert data.inner.len == 5
-	assert data.inner[0] == 1.0
-	assert data.inner[4] == 5.0
-	assert data.test == 1.2
-
-	data_json := json.encode(data)
-	dump(data_json)
-	assert data_json == str
-}