Allocator: allocBytes and reallocBytes

[leecannon]

Reimplement reallocBytes after regression from #9394/#10112
Also adds an analogous allocBytes function.

@silversquirl / @mlugg: do these functions satisfy your requirements?
As the these functions don't return a slice with the alignment as part of the type I choose not to name them something like reallocAdvancedWithRetAddrRuntimeAlignment to seperate them from the other alloc/realloc functions.

closes #10348

[mlugg]

Quickly skimming through, it looks like that should be fine for my use case yeah. Thanks!

[andrewrk]

Thanks for the patch!

Needs simple test coverage and then it's good to go.

[leecannon]

Tests added

[andrewrk]

Thank you 👍