[JDK9] RFR 8167229: Improve VarHandle documentation

[Martin Buchholz]

Looks good!

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Consider changing parameter name of findVarHandle name to make it clearer
it's a field name
name => fieldName
findVarHandle(Class<?> recv, String name, Class<?> type)

I might have named these methods instanceFieldVarHandle and
staticFieldVarHandle to make it clearer there are many kinds of VarHandle
and ways of obtaining them.  But probably too late now.

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it's => its

1921          * {@code volatile} declaration) in accordance to it's
specified
1922          * access modes.