6921740: Eliminate warnings from sun.io converters and allow compiling with JAVAC_MAX_WARNINGS=true
Summary: Fix sun.io converters unchecked and cast warnings produced by -Xlint:all
Reviewed-by: alanb, sherman
^build/
^dist/
/nbproject/private/
^src/share/tools/hsdis/build/
^src/share/tools/IdealGraphVisualizer/[a-zA-Z0-9]*/build/
^src/share/tools/IdealGraphVisualizer/build/
^src/share/tools/IdealGraphVisualizer/dist/