Sponsor Request: 8241100: Make Boolean, Character, Byte, and Short implement Constable

[Jorn Vernee]

Hi,

Can someone please sponsor this patch that makes Boolean, Character, 
Byte, and Short implement Constable?

Bug: https://bugs.openjdk.java.net/browse/JDK-8241100
Webrev: http://cr.openjdk.java.net/~jvernee/8241100/webrev.00/

Having the other box types implement Constable makes them easier to use 
with APIs that accept any Constable. Though I'm mostly interesting in 
boolean, for which I'm currently falling back to "true" & "false" 
strings, but the downside is that this also requires parsing the string 
again and having to deal with random other strings.

This patch also adds the ConstantBootstraps::convert method that is used 
to facilitate the conversion from int to (short|char|byte). This 
currently takes a source type explicitly. In practice, it seems that 
Object can always be used as a source type for the same behavior, but 
explicitly specifying source and destination types seems more robust to 
me in case this behavior ever changes, or we want to expand on the 
supported kinds of conversion. (for instance it is currently not 
possible to convert from an int to a Long directly, or from Short to 
Integer, but maybe those cases could be supported in the future as well).

Testing: tier1-3 & downstream testing for my particular use case

Thanks,
Jorn