RFR: 8204610: Compiler confused by parenthesized "this" in final fields assignments

[Maurizio Cimadamore]

Hi,
this patch fixes the problem we have been talking about yesterday [1].

Basically, javac does not consistently skip parenthesis when enforcing 
foward refs and DA/DU rules.

I decided to consolidate the 'is this a variable name, possibly 
qualified by "this" ', into a separate TreeInfo routine, and call that 
from Flow and Attr (it turned out that the wrong logic was applied in 
both places).

I have included a combo test which tests several combinations of the kind

((this).(x)) = 1

This might include (as in the example above, as the selected variable 
symbol can't be wrapped in its own parenthesis) nonsensical combination, 
which the test makes sure they are rejected.

Webrev:

http://cr.openjdk.java.net/~mcimadamore/8204610/

Cheers

Maurizio

[1] - 
http://mail.openjdk.java.net/pipermail/compiler-dev/2018-June/012005.html