luci-lua-runtime: also search luci.dispatcher scope when looking up values

Some legacy templates access dispatcher functions such as `build_url()`
without explicit scope, which worked in the old runtime since the template
view namespace was instantiated from the dispatcher.

Ensure that this continues to function in the emulated runtime.

Fixes: #6082
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

modules/luci-lua-runtime/luasrc/template.lua

@@ -121,7 +121,7 @@ context.viewns = setmetatable({
 	elseif key == "resource" then
 		return L.config.main.resourcebase
 	else
-		return rawget(tbl, key) or _G[key] or L[key]
+		return rawget(tbl, key) or disp[key] or _G[key] or L[key]
 	end
 end})