Extract Windows string_conversion target (#26029)
Extract Windows string_conversion target (#26029)

String conversion between UTF-8 and UTF-16 encodings is useful even in
the absence of other common Windows functionality.

This is pre-factoring for uwptool, which adds an adb-like helper tool
for install, uninstall, and launch of UWP applications for Windows
platforms.

See: https://github.com/flutter/flutter/issues/81756
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