Use web-time to return a SystemTime that works under WASM

The `MilliSecondsSinceUnixEpoch::to_system_time()` method returns the
`SystemTime` type from the standard library.

The `std::time::SystemTime::elapsed()` method sadly panics under WASM.
Instead of returning the `SystemTime` from the standard library we're
now returning a drop-in replacement of this type coming from the web-time
crate.

crates/ruma-common/CHANGELOG.md

@@ -14,6 +14,9 @@ Breaking changes:
 
 Improvements:
 
+- Use the [web-time](https://github.com/daxpedda/web-time) crate to return a
+  `SystemTime` that works under WASM in the
+  `MilliSecondsSinceUnixEpoch::to_system_time()` method.
 - Stabilize support for `.m.rule.suppress_edits` push rule (MSC3958 / Matrix 1.9)
 - Add `MatrixVersion::V1_9`
 - Point links to the Matrix 1.9 specification

crates/ruma-common/Cargo.toml

@@ -77,6 +77,7 @@ time = "0.3.34"
 tracing = { workspace = true, features = ["attributes"] }
 url = "2.2.2"
 uuid = { version = "1.0.0", optional = true, features = ["v4"] }
+web-time = "1.1.0"
 wildmatch = "2.0.0"
 
 [target.'cfg(all(target_arch = "wasm32", target_os = "unknown"))'.dependencies]

crates/ruma-common/src/time.rs

@@ -1,11 +1,12 @@
 use std::{
     fmt,
-    time::{Duration, SystemTime, UNIX_EPOCH},
+    time::{Duration, UNIX_EPOCH},
 };
 
 use js_int::{uint, UInt};
 use serde::{Deserialize, Serialize};
 use time::OffsetDateTime;
+use web_time::SystemTime;
 
 /// A timestamp represented as the number of milliseconds since the unix epoch.
 #[derive(Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord, Deserialize, Serialize)]