Add sdk support for SAC trust() (#1824)

### What

Add support for CAP-0073

Author: sisuresh

soroban-sdk/src/token.rs

@@ -469,4 +469,23 @@ pub trait StellarAssetInterface {
     /// Emits an event with topics `["clawback", admin: Address, to: Address],
     /// data = amount: i128`
     fn clawback(env: Env, from: Address, amount: i128);
+
+    /// Creates this contract asset's unlimited trustline for the provided
+    /// address.
+    ///
+    /// This is a no-op if the input address is a C-address, or if the
+    /// provided G-address already has the respective trustline.
+    ///
+    /// If the trustline is actually created, this will require authorization
+    /// from `addr` (i.e. `addr.require_auth` will be called).
+    ///
+    /// # Arguments
+    ///
+    /// * `addr` - The address for which a trustline will be created.
+    ///
+    /// # Panics
+    ///
+    /// Panics during trustline creation if the asset issuer does not exist,
+    /// or when a new trustline cannot be created.
+    fn trust(env: Env, addr: Address);
 }

stellar-asset-spec/src/lib.rs

@@ -38,6 +38,7 @@ pub(crate) const XDR_INPUT: &[&[u8]] = &[
     &soroban_sdk::token::StellarAssetFnSpec::spec_xdr_symbol(),
     &soroban_sdk::token::StellarAssetFnSpec::spec_xdr_transfer(),
     &soroban_sdk::token::StellarAssetFnSpec::spec_xdr_transfer_from(),
+    &soroban_sdk::token::StellarAssetFnSpec::spec_xdr_trust(),
     &soroban_token_sdk::events::Approve::spec_xdr(),
     &soroban_token_sdk::events::TransferWithAmountOnly::spec_xdr(),
     &soroban_token_sdk::events::Transfer::spec_xdr(),
@@ -53,7 +54,7 @@ pub(crate) const XDR_INPUT: &[&[u8]] = &[
     &SetAuthorized::spec_xdr(),
 ];
 
-pub(crate) const XDR_LEN: usize = 8560;
+pub(crate) const XDR_LEN: usize = 9128;
 
 /// Returns the contract spec for Stellar Asset contract.
 pub const fn xdr() -> &'static [u8] {