[zircon] non-resizable VMOS

This CL introduces the first option for VMO creation
ZX_VMO_NOT_RESIZABLE that 'locks' the size of a root (non-clone) VMO

Also enables the same for COW clones via ZX_VMO_CLONE_NON_RESIZEABLE

This is meant to answer safety hazards of having a client pass
VMOs to servers which the client can resize while the server is
copying data into via a memory map.

Today this is done via ZX_INFO_HANDLE_COUNT but that turns out
is racy.

This CL also cleans up vmo-tests so they using proble_for_read
and probe_for_write instead of using unrelated syscalls to test
memory mappings.

TEST=added unittests in vmo_tests

ZX-2279 #comment progress

Change-Id: If69ce772dcccd92db83f5bda313ae2343ebb448e

[kernel][vm] move vm.h to the new spot and remove some unused code

Change-Id: I69f1b804fb95dd44e3e0619943e8809519aa82ca

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[kernel][arena] Add diagnostic count to fbl::{Arena,TypedArena}

Change-Id: I8e8977b4ac1e529020991e4c8fd3fd0519d9537f

[zircon][mxtl->fbl] Rename mxtl to fbl

Change-Id: Ie21b6498e1bfb0a7fa0315e40b9e5c3ee78646be