[patterns] Draft Spec for JEP 375 Pattern Matching for instanceof (Preview 2)

[Gavin Bierman]

Dear experts:

The latest (and hopefully final) draft of JEP 375 (Pattern matching for
instanceof) is available at:

    http://cr.openjdk.java.net/~gbierman/jep375/latest

This spec is now equivalent to the spec for the first preview version (JEP 305). 
The only changes are:

1. Some minor typos corrected. 

2. Added missing case dealing with parenthesized expressions in the definition
of scope of pattern variables.

3. Added missing case dealing with labeled statements in the definition of scope
of pattern variables.

We have decided to remove the deconstruction patterns for record types from this
preview release. There are some complications surrounding generics and
deconstruction patterns, along with varargs and deconstruction patterns, and
we'd like some more time to consider our design. I'll write separately on these
issues.

Thanks,
Gavin