Expensive teleports

[gilescope]

#2102 has landed now that XCM v3 has arrived.

However the integration tests show that a limited_teleport_assets can be expensive (38bn weight). This is due to Wild(All) being used here: https://github.com/paritytech/polkadot/blob/bebd1a788ecccfa1a6adc61004e4f700988f40d4/xcm/pallet-xcm/src/lib.rs#L1207 - this means we multiply the weight by max assets (which is currently 100).

Could we change the code there so that it can sometimes issue Wild(AllOf) potentially as that has drastically lower fees?