flex/before quirk in IE/11.483 and Edge/40.15063

the characters shown below are the space separators (Zs) as of Unicode 10.0
test cases shown in yellow are expected to change when white-space changes
test cases shown in black are not expected to change when white-space changes

before		after
block	flex	block	flex
< 3 × U+0020 >	< 3 × U+0020 >	< 3 × U+0020 >	< 3 × U+0020 >
< 3 × U+00A0 >	< 3 × U+00A0 >	< 3 × U+00A0 >	< 3 × U+00A0 >
< 3 × U+1680 >	< 3 × U+1680 >	< 3 × U+1680 >	< 3 × U+1680 >
< 3 × U+2000 >	< 3 × U+2000 >	< 3 × U+2000 >	< 3 × U+2000 >
< 3 × U+2001 >	< 3 × U+2001 >	< 3 × U+2001 >	< 3 × U+2001 >
< 3 × U+2002 >	< 3 × U+2002 >	< 3 × U+2002 >	< 3 × U+2002 >
< 3 × U+2003 >	< 3 × U+2003 >	< 3 × U+2003 >	< 3 × U+2003 >
< 3 × U+2004 >	< 3 × U+2004 >	< 3 × U+2004 >	< 3 × U+2004 >
< 3 × U+2005 >	< 3 × U+2005 >	< 3 × U+2005 >	< 3 × U+2005 >
< 3 × U+2006 >	< 3 × U+2006 >	< 3 × U+2006 >	< 3 × U+2006 >
< 3 × U+2007 >	< 3 × U+2007 >	< 3 × U+2007 >	< 3 × U+2007 >
< 3 × U+2008 >	< 3 × U+2008 >	< 3 × U+2008 >	< 3 × U+2008 >
< 3 × U+2009 >	< 3 × U+2009 >	< 3 × U+2009 >	< 3 × U+2009 >
< 3 × U+200A >	< 3 × U+200A >	< 3 × U+200A >	< 3 × U+200A >
< 3 × U+202F >	< 3 × U+202F >	< 3 × U+202F >	< 3 × U+202F >
< 3 × U+205F >	< 3 × U+205F >	< 3 × U+205F >	< 3 × U+205F >
< 3 × U+3000 >	< 3 × U+3000 >	< 3 × U+3000 >	< 3 × U+3000 >