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/src/extension_api.rs

@@ -22,6 +22,7 @@ pub use wit::{
     zed::extension::dap::{
         DebugAdapterBinary, DebugRequest, DebugTaskDefinition, StartDebuggingRequestArguments,
         StartDebuggingRequestArgumentsRequest, TcpArguments, TcpArgumentsTemplate,
+        resolve_tcp_template,
     },
     zed::extension::github::{
         GithubRelease, GithubReleaseAsset, GithubReleaseOptions, github_release_by_tag_name,