RFR: JDK-8282008: Incorrect handling of quoted arguments in ProcessBuilder

[Roger Riggs]

Quoting related changes in https://bugs.openjdk.java.net/browse/JDK-8250568 modified the way that
process builder recognized argument strings, causing some arguments to be doubly quoted and malformed.

ProcessBuilder encodes command arguments in two ways, a looser legacy encoding
and stricter encoding that prevents quotes from being misinterpreted.
The system property jdk.lang.Process.allowAmbiguousCommands controls which is in effect.

When the property is "true" or not set, arguments are inserted into the Windows command line
with minimal changes.  Arguments containing space or tab are quoted to prevent them being split.
Arguments that start and end with double-quote are left alone.
Some executables interpret a backslash before the final quote as an escape; if the argument 
contains first and last quotes, backslashes are ignored.

When the allowAmbigousCommands property is `false`, care is taken to ensure that
the final quote of an argument is the closing quote for the argument and is not
interpreted as a literal quote by a preceding quote (or an odd number of quotes).

The PR includes a test matrix of the cases where an argument with spaces and a final backslash
is passed with each combination of `allowAmbiguousCommands = true and false`,
launched executable, java, .cmd, and .vbs and when the argument is surrounded with double-quotes.

The priority for allowAmbiguousCommands = false is that no argument is split or joined to another argument.
In some cases, backslashes are doubled to prevent a double-quote from being interpreted incorrectly.
The trailing backslash in an argument occurs rarely exception when the argument is a directory.
In that case, the addition of trailing backslashes is benign when the string is used as a filesystem path.

See also PR#7504, for background and a proposal.

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Commit messages:
 - Cleanup comment and copyright
 - JDK-8282008: Incorrect handling of quoted arguments in ProcessBuilder

Changes: https://git.openjdk.java.net/jdk/pull/7709/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7709&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282008
  Stats: 341 lines in 2 files changed: 330 ins; 6 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7709.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7709/head:pull/7709

PR: https://git.openjdk.java.net/jdk/pull/7709