Description:
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The official Windows builds do not support the DOTNET class.
Apparently, they are compiled on a system where mscoree.h is not
available[1].

It seems to me that it is sufficient to document this issue.

[1] <https://windows.php.net/downloads/snaps/php-7.3/r03f6b16/logs/configure-ts-windows-vc15-x64-r03f6b16.txt>

Test script:
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<?php

echo (!extension_loaded('com_dotnet') || class_exists('DOTNET')) ? 'ok' : 'hmm';

Expected result:
----------------
ok

Actual result:
--------------
hmm