[debuglog] Migrate to zx_debuglog_create

Test: cq

Change-Id: Ia7aa2efefd0c1ac0ce3460159a9405d6f0b1777e

[fs-management] Refactor filesystem launching code

- Deduplicate nearly all code used between the different mechanisms
to initialize a filesystem process.
- Add the ability to launch a filesystem process without any
stdio. This may be useful for tests which provoke filesystem
errors, and might provide noisy test output.

Test: fs-management

Change-Id: I3171bc511fd99a2e0503064b03db57ca5b8ed64c

[fs-management] Switch to fdio_spawn_etc

Most codepaths that create processes should use fdio_spawn rather than
launchpad directly.

Test: No behavior change
Change-Id: I000e1e48359e8a46613961afb2c1ed482d4e9335

[fdio] Move headers into lib/fdio/...

Change-Id: Ie8d74e716da913bf6e2672c4acf8cd67b4962b7f

[zx] Move public zx headers to match naming convention

The zx library provides headers intended for general use, so the
include path should be spelled <lib/zx/foo.h> as per
https://fuchsia.googlesource.com/docs/+/master/development/languages/c-cpp/naming.md.
This moves the headers into the proper location and updates includes to
match.

Change-Id: I6fc9b2a491b5f8b0d270c4dfc77fa4be5739071b

[zx] Update callers to zx::time and zx::duration types

The zx_time_t and zx_duration_t variants will be removed eventually.

Change-Id: Icc54983edc154eee2d1258160f921c3afc212ae0

Clean up sloppy zx_handle_t/integer conflation

Change-Id: I5659232efa8531ef97261639cc65f211ee9f0cc8

[storage] Use some cpp constructs on fs-management code.

ZX-1381

Change-Id: I9b1febab85ec43c2cdbbc8c03fa5c1139d7e1501

[storage] Rename some fs-management files from c to cpp.

ZX-1381

Change-Id: Ife8979017ca4af07e5d3b2e992af667d7271dcc9