Button font can't have All-Uppercase in Material Theme at Windows.

Please refer to the following forum issue.

https://forum.qt.io/topic/97974/qt-quick-control-2-material-theme-upper-case-are-in-lower-case-on-windows-qt-5-12-0

It isn't clearly described in the Google Materials Design Guide, it seems that it is a specification that button text have an all uppercase.
I confirm android at API21, Button font capitalization had set all uppercase.

/sdk/platforms/android-21/data/res/values/styles_material.xml

<style name="TextAppearance.Material.Button">
    <item name="textSize">@dimen/text_size_button_material</item>
    <item name="fontFamily">@string/font_family_button_material</item>
    <item name="textAllCaps">true</item>
    <item name="textColor">?attr/textColorPrimary</item>
 </style>

Currently, Ubuntu can view All-Uppercase button text,
but,on Windows, it mixed Uppercase / lowercase.