Add support for generating --help messages from cmdline definition

Previously our --help messages were always simply hard-coded text
blocks. This makes it easy for them to get out-of-sync with the actual
flags the programs take. To fix this teach the cmdline system how to
generate these types of help text.

Convert over `dalvikvm` which is one of the worst when it comes to
usefulness of the -help text.

```
% dalvikvm -help
dalvikvm: [options] class [argument ...]

The following standard arguments are supported:
  -classpath {string value}
  -cp {string value}
    The classpath, separated by ':'
  -D{string value} [-D{string value}...]
  -verbose:{class|collector|compiler|deopt|gc|heap|interpreter|jdwp|jit|jni|monitor|oat|profiler|signals|simulator|startup|third-party-jni|threads|verifier|verifier-debug|image|systrace-locks|plugin|agents|dex}
    Switches for advanced logging. Multiple categories can be enabled separated by ','. Eg: -verbose:class,deopt
  -help
  -h
    Print this help text.
  -showversion
  -agentpath:{/path/to/libagent.so=options} [-agentpath:{/path/to/libagent.so=options}...]
    Load native agents.
The following extended arguments are supported:
  -Xbootclasspath:{list separated by ':'}
  -Xcheck:jni
  -Xms{Memory with granularity of 1024 bytes}
  -Xmx{Memory with granularity of 1024 bytes}
  -Xss{Memory with granularity of 1 bytes}
  -Xint
The following Dalvik arguments are supported:
  -Xzygote
    Start as zygote
  -Xjnitrace:{string value}
...
```

Test: dalvikvm -help
Bug: 160933150
Change-Id: Id96bc8340b799636d322450cb95c88f814a77c35

0 files changed, 0 insertions, 0 deletions