`start` should query the page size right away instead of on the first call to `pageSize()`

[Trevor-Strong]

Just what the title says. The page size is fundamentally a constant for a given machine, so heap.pageSize() could be
implemented as a simple read from a global variable instead of needing to lookup the page size the first time its called and needing to use atomics. On every system I'm aware of, getting the page size is relatively easy to do so the startup
overhead should be minimal. This could even be done conditionally based on whether or not the user has replaced the options.queryPageSize function or not.

On Linux, at least, this is basically free since we are getting the page size from the auxiliary vector, and the start
code already iterates the entire aux vector anyways.

[alexrp]

The current code is nice because it's simple and works everywhere. There is no start code in the case of a library, meaning we'd have to maintain the current code for that case, in addition to what you're proposing here. I think I'd want to see some performance measurements to be convinced that that's worth it.