Expose rust code gen of contracts without the file import (#1311)

### What
Expose rust code gen of contracts without the file import.

### Why
The code gen function for rust code generates the interface and types as
well as an import of the wasm binary. The CLI uses this function and
wants to output the generated code without the wasm binary.

Related to:
-
stellar/stellar-cli#1532 (comment)

soroban-spec-rust/src/lib.rs

@@ -57,6 +57,14 @@ pub fn generate_from_wasm(
 }
 
 pub fn generate(specs: &[ScSpecEntry], file: &str, sha256: &str) -> TokenStream {
+    let generated = generate_without_file(specs);
+    quote! {
+        pub const WASM: &[u8] = soroban_sdk::contractfile!(file = #file, sha256 = #sha256);
+        #generated
+    }
+}
+
+pub fn generate_without_file(specs: &[ScSpecEntry]) -> TokenStream {
     let mut spec_fns = Vec::new();
     let mut spec_structs = Vec::new();
     let mut spec_unions = Vec::new();
@@ -81,8 +89,6 @@ pub fn generate(specs: &[ScSpecEntry], file: &str, sha256: &str) -> TokenStream
     let error_enums = spec_error_enums.iter().map(|s| generate_error_enum(s));
 
     quote! {
-        pub const WASM: &[u8] = soroban_sdk::contractfile!(file = #file, sha256 = #sha256);
-
         #[soroban_sdk::contractclient(name = "Client")]
         #trait_