The monotonic clock may be too underspecified

The monotonic clock as it stands right now is likely too underspecified in what it is measuring and should possibly be split into two separate clocks. This problem is something that is fairly unknown, but eventually has bitten basically every operating system, browser and programming language and I would want to prevent WASI from running into the same issue before it's too late.

The thing is that a lot of programs want to measure the time they are actively running, whereas a lot of programs want to measure the real world time that is happening. That sounds like it is the same thing, but it actually differs when the host is suspended (phone screen turned off, laptop closed, operating system suspended, wasm runtime suspending the guest module for a while, ...).

A lot of the time you want to measure the actual real world time that has progressed, for example when you have some sort of server API token that expires in 60 minutes, then turning off the screen of my phone for a while shouldn't mess with the time measurement.

However there are also cases where an application wants to only measure "its perceived time". The easiest example would be in a game, where me turning off the screen of my phone and turning it back 20 minutes later shouldn't cause the physics to freak out because a single frame took 20 minutes (usually the velocity vectors are multiplied by the time a frame takes).

Whether this second case is worth supporting in WASI is debatable, but it's important to at least very clearly state the difference in the documentation, such that runtime implementations don't accidentally implement the wrong thing. In fact the WebAssembly runtimes (such as wasmtime) already inconsistently implement this as either "real time" or "perceived time".

References:
https://lwn.net/Articles/428176/
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d6ed449afdb38f89a7b38ec50e367559e1b8f71f
https://kernel.googlesource.com/pub/scm/linux/kernel/git/stable/linux-stable/+/a3ed0e4393d6885b4af7ce84b437dc696490a530
https://github.com/rust-lang/rust/issues/87906
https://github.com/golang/go/issues/24595
https://github.com/w3c/hr-time/issues/115
https://bugs.chromium.org/p/chromium/issues/detail?id=1206450
https://bugzilla.mozilla.org/show_bug.cgi?id=1709767
https://bugs.webkit.org/show_bug.cgi?id=225610

No source files, tests, or entry points are named. Start by reviewing the existing WASI monotonic-clock specification and the linked operating-system and runtime references. Done means reaching and documenting a clear decision about real-world versus perceived elapsed time, including whether separate clocks are needed.