EXT-8318 ADDITIONAL FIXED ensure that thousands separator is in utf8 format (on Windows) before converting it to LLWString.

Problem on Windows:
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LLPanelMainInventory::updateItemcountText() formats number using viewer locale.
non-break space is detected as unknown symbols while converting utf8str_to_wstring when formatted text is set to LLTextBox.

FIX:
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Added converting of string to multi-byte string and then to utf8 string while formatting on Windows.
  created opposite to "ll_convert_wide_to_string" function "ll_convert_string_to_wide" and helper function to call both of them.
  It is used now to convert result of formatted string while formatting integer number in locale.

Fix affects Windows only.

Reviewed by Richard Nelson at https://codereview.productengine.com/secondlife/r/775/

--HG--
branch : product-engine