[zx][dash] Rename dash commands to use zx-style prefixes

Change-Id: I6011a451da9e9cd867d0089b344eaa81dcff938c

[dash] remove '@' builtin

Change-Id: Icf2f2459da94766bb250cca72923ebad3df3642a

[dash] Run builtin ls, cp, mv, etc last

This change lets clients replace the built-in versions of ls and the other core
utils with more complete versions.

Change-Id: I6d7b0c1bdd1d3f56199034c15c60cb983cb2b006

[dash] Improve mv support

Add -f option, and support for moving from multiple files to a
directory.

Change-Id: I11c2511c5ef4eb32a58c98e3bf19e358c7296ecb

[dash] fix mv builtin

A previous commit introduced the source for the builtin but did not
regenerate the files needed to integrate the builtin.

Change-Id: I2ff31dc8a8099a46a1a0a0d18cf7f2fe45335bf6

[uapp][dash] remove the kill command and regenerate the builtins

Change-Id: I17812956643d5b09b87e79757f1a4260e0a005c5

[dash] Add builtin @ command

The @ command lets you interact with the Fuchsia application manager.
This command matches mxsh.

Change-Id: Iffe848f46f80db15a78c1bb1804794e9f02e9239

[dash] Add builtin k function

The k function triggers a kerneldebug command, similar to ` in mxsh. We
can't use ` in dash because ` is a control character in Bourne shells.

Change-Id: I179ef72170b2a4b7a35e83f78181826397fa5f19

[dash] import builtins from mxsh

Change-Id: I288ae52d15332820ade51c2e764b9a28825ca8af

[dash] Add dash to the build

This patch integrates dash with the build system, including
pre-generating source files.

Change-Id: If19d0be0c030c6c194cb7bf66a26be48a39c0847