pkg/web: restrict handler types (#48495)

Makes `pkg/web` only accept handles from the following set:

```go
	handlerStd       = func(http.ResponseWriter, *http.Request)
	handlerStdCtx    = func(http.ResponseWriter, *http.Request, *web.Context)
	handlerStdReqCtx = func(http.ResponseWriter, *http.Request, *models.ReqContext)
	handlerReqCtx    = func(*models.ReqContext)
	handlerReqCtxRes = func(*models.ReqContext) Response
	handlerCtx       = func(*web.Context)
```

This is a first step to reducing above set to only `http.Handler`.

---

Due to a cyclic import situation between `pkg/models` and `pkg/web`, parts of this PR were put into `pkg/api/response`, even though they definitely do not belong there. This however is _temporary_ until we untangle `models.ReqContext`.

pkg/web/macaron.go

@@ -19,9 +19,10 @@
 package web
 
 import (
+	_ "unsafe"
+
 	"context"
 	"net/http"
-	"reflect"
 	"strings"
 )
 
@@ -47,31 +48,14 @@ func Version() string {
 // and panics if an argument could not be fulfilled via dependency injection.
 type Handler interface{}
 
-// handlerFuncInvoker is an inject.FastInvoker wrapper of func(http.ResponseWriter, *http.Request).
-type handlerFuncInvoker func(http.ResponseWriter, *http.Request)
-
-func (invoke handlerFuncInvoker) Invoke(params []interface{}) ([]reflect.Value, error) {
-	invoke(params[0].(http.ResponseWriter), params[1].(*http.Request))
-	return nil, nil
-}
+//go:linkname hack_wrap github.com/grafana/grafana/pkg/api/response.wrap_handler
+func hack_wrap(Handler) http.HandlerFunc
 
 // validateAndWrapHandler makes sure a handler is a callable function, it panics if not.
 // When the handler is also potential to be any built-in inject.FastInvoker,
 // it wraps the handler automatically to have some performance gain.
 func validateAndWrapHandler(h Handler) Handler {
-	if reflect.TypeOf(h).Kind() != reflect.Func {
-		panic("Macaron handler must be a callable function")
-	}
-
-	if !IsFastInvoker(h) {
-		switch v := h.(type) {
-		case func(*Context):
-			return ContextInvoker(v)
-		case func(http.ResponseWriter, *http.Request):
-			return handlerFuncInvoker(v)
-		}
-	}
-	return h
+	return hack_wrap(h)
 }
 
 // validateAndWrapHandlers preforms validation and wrapping for each input handler.