RFR 8200199: javac suggests to use var even when var is used

[Maurizio Cimadamore]

Hi,
there is an issue with the local variable inference finder: the finder 
reports possible cases where 'var' could be used even when the developer 
has already used 'var'. This is due to a timing issue with which the 
analyzer runs - by the time it runs, variable types have already been 
written into the AST by Attr - so the call to 
JCVarDecl.isImplicitlyTyped() is moot, as that call will simply look to 
see as to whether the tree type == null.

Since the var types corresponding to implicitly inferred types are 
synthetic and have no position set (see Attr::setSyntheticVariableType) 
I decided to use that property instead to decide as to whether the 
analyzer should, or should not consider a given variable declaration. 
This seems to be a good pragmatic solution. In the long run we should 
probably consolidate the treatment of implicitly inferred variables, and 
have some kind of common way to speak about them (e.g. both locals and 
implicit lambda parameters).

Webrev:
http://cr.openjdk.java.net/~mcimadamore/8200199/

Cheers
Maurizio