Use DecodeLimit for decoding XCM messages

[KiChjang]

Fixes paritytech/srlabs_findings#117.

This PR upgrades parity-scale-codec to 2.3.0 (to pick up decode_and_advance_with_depth_limit) and adds an upper limit on the length of the XCM messages during decoding.

[bkchr]

Here we don't really want to advance the data? We more want to decode all the data, otherwise it should be an error?

[KiChjang]

Ah ok, so decode's default behaviour is to advance the cursor, albeit without any upper limit to the input data length, but if we wanna change the behaviour to "decode everything otherwise error", we can change that too.

[KiChjang]

"/tmp/.tmpFzXtH6/chains/local_testnet/db/full" removed.
"/tmp/.tmpFzXtH6/polkadot/chains/westend2/db/full" did not exist.
test purge_chain_works ... FAILED
failures:
---- purge_chain_works stdout ----
thread 'purge_chain_works' panicked at 'assertion failed: !base_path.path().join(\"chains/local_testnet/db\").exists()', polkadot-parachains/tests/purge_chain_works.rs:74:9
stack backtrace:
   0: rust_begin_unwind
             at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/panicking.rs:493:5
   1: core::panicking::panic_fmt
             at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/core/src/panicking.rs:92:14
   2: core::panicking::panic
             at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/core/src/panicking.rs:50:5
   3: core::ops::function::FnOnce::call_once
   4: core::ops::function::FnOnce::call_once
             at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/core/src/ops/function.rs:227:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
failures:
    purge_chain_works
test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 31.05s
error: test failed, to rerun pass '-p polkadot-collator --test purge_chain_works'

Unsure what went wrong with CI here? Retried a couple of times, but the problem still persists.

[bkchr]

The error is known and needs to be fixed. However, it only appears on ci