[docs][syscalls] Add TODOs about documenting system call rights

ZX-2399 #comment

Test: no functional change
Change-Id: I1f285c677e2444fcf1d720d7ecbd9f490c303962

[docs][syscalls] Clarify ZX_ERR_NO_MEMORY as eventually going away

Not touched:
vmo_op_range.md
vmo_set_size.md
vmo_write.md
The current text is ok for these.

ZX-2303 #comment patch

Tested: Just doc changes, read before/after.

Change-Id: I2c6e1039e2b205e9cc377b9888755fa7ac676c78

[syscalls] Remove read_status from zx_channel_call

This parameter no longer has a purpose. Also, remove ZX_ERR_CALL_FAILED.
This status code no longer has a purpose.

Test: No behavior change
Change-Id: I71945ea9d1d6d591a20476106df1e598dfaf97b1

[syscalls] zx_channel_call should always consume handles

Previously, whether zx_channel_call consumed handles depended on whether
it succeeded or failed.

ZX-2204 #comment

Test: utest/core/channel

Change-Id: Ic7b1149a85a1a892144479ee2f543fc7fedc6114

[syscall][channel_call] use kernel allocated txids

This removes the need for channel_call() users to generate unique
txids for each channel_call() invocation. Instead, the kernel will
allocate a suitable txid in the 0x80000000..0xFFFFFFFF space (leaving
0..0x7FFFFFFF for userspace message processors to use when doing
such "calls" via channel_write() in a non-conflicing manner)

Update unit tests to deal with the new reality.

Change-Id: If4483df60179320c4f75ae1fe77f46035859fcc4

Fix typo in channel_call documentation

Bug:
Change-Id: I514783a6b6771f0b38c951608421a24f2122879a

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[docs] Fix grammar nit in use of "any"

"any of *handles* are..." sounds odd. This is complicated by the
convention that a variable name noun phrase is usually singular (an
example is the sentence "*handles* is a variable of pointer type").

Resolve any ambiguity here by saying "any element in *handles*".

Change-Id: I36b3579805043967c2b89c59e5858c00377ca6f8

Fix spelling of "occurred"

Change-Id: Id50ee3b87e1712558790aa44b99737a5961122da

[docs][errors] Rename all the errors in docs/ to MX_OK and MX_ERR_*

Change-Id: I62451456a83145760c6454a619d4c699ce8e9017

[syscalls] Switch all syscall interfaces to deadlines

Change-Id: If1c2540b7aa3d16e8080551100b19fb1a067be8c

[errors] stop using deprecated ERR_HANDLE_CLOSED

Instead use ERR_CANCELED, its new name.

Change-Id: I2671a6eded761b6b06737c93b3289c2b8a46d8bd

[magenta][errors] Rename ERR_REMOTE_CLOSED to ERR_PEER_CLOSED

This error, at least at the Magenta syscall level, is really about
peers. This new name aligns with the MX_*_PEER_CLOSED signals. And
REMOTE implies a distance or asymmetry that isn't necessarily true.

This leaves a compatibility alias for the old name in place until the
rest of Fuchsia can be cleaned up.

Change-Id: Icf95003b2813270d865c6876b62e21d9f5b8c0f6

[types][transaction] Name the transaction ID type.

We've discussed potentially moving this to 8 bytes as part of the
FIDLv2.0 work.

Change-Id: I510064cfe231cda09163759d9b4247682d8300e9

[syscalls] Uniformally use "options" rather than "flags" as a syscall parameter name

With the exception of the VMAR syscalls which really do want to talk
about map_flags.

Part of MG-559

Change-Id: I51673de824b4072990f01724a3bf522a9a84f4f4

[docs][syscalls] Fix all the manpages

Change-Id: Ie9ba25060f3331de8d9c178caf6332fb48fc80f5

[syscalls] rename mx_handle_wait_*() to mx_object_wait_*()

These act on the object the handle refers to, not the handle itself.

Compatibility wrappers are provided to ensure existing code
continues to compile, link, and run. Later we will deprecate
the wrappers and eventually remove them.

Change-Id: Icf69e75f7e0c060ba6026343f9d26ff9da4317d9

[magenta][syscalls] implement mx_channel_call()

This is a fused write-wait-read syscall for the use of synchronous rpc
callers. The kernel treats the first uint32_t of the outbound message
as a transaction ID and accepts an inbound message with a matching txid
as a reply, completing the transaction.

This allows multi-threaded calling of synchronous rpc transports
with no userspace bookkeeping required and will provide an opportunity
for smarter scheduling of such transactions in the future.

Change-Id: Ifbb92b36618ebf13a6e52c650d16fed9f5071c3a