extension/dap: Add resolve_tcp_template function (#31010)

Extensions cannot look up available port themselves, hence the new API.
With this I'm able to port our Ruby implementation into an extension.

Release Notes:

- N/A

crates/extension_api/wit/since_v0.6.0/dap.wit

@@ -1,6 +1,9 @@
 interface dap {
     use common.{env-vars};
 
+    /// Resolves a specified TcpArgumentsTemplate into TcpArguments
+    resolve-tcp-template: func(template: tcp-arguments-template) -> result<tcp-arguments, string>;
+
     record launch-request {
         program: string,
         cwd: option<string>,