To fix bogus MSVC warnings:

  c:\projects\harfbuzz\src\hb-array.hh(189): warning C4521: 'hb_array_t<Type>': multiple copy constructors specified [C:\projects\harfbuzz\build\harfbuzz.vcxproj]
  c:\projects\harfbuzz\src\hb-array.hh(189): warning C4522: 'hb_array_t<Type>': multiple assignment operators specified [C:\projects\harfbuzz\build\harfbuzz.vcxproj]

If they're not, it's a bug in our subsetting logic somewhere.  So check.

Calls obj.copy() or obj.operator=() in that order.

The first three based on range-v3.

Delete assignment operator of OffsetTo<> instead of Offset<>.

In simple ArrayOf<>::sanitize() assert that Type has assignment operator.
Ideally we should SFINAE this and fallback to calling Type::sanitize()
if assignment operator is not available.  But we don't have a case of
that in the codebase.

Fixes https://github.com/harfbuzz/harfbuzz/issues/1651

Just sending this to bots to see if all happy, then turn it into macro and
apply everywhere.

Part of https://github.com/harfbuzz/harfbuzz/issues/1651

Jenga.

Part of https://github.com/harfbuzz/harfbuzz/issues/1652

This reverts commit 98f14c4c.

Same as previous commit.