Move some code of LocalizedNumberICU.cpp to ICULocale.cpp

Move some code of LocalizedNumberICU.cpp to ICULocale.cpp
https://bugs.webkit.org/show_bug.cgi?id=84128

Reviewed by Hajime Morita.

No new tests. No behavior change.

* WebCore.gypi: Add ICULocale.cpp
* platform/text/ICULocale.cpp:
Added. Move some code from LocalizedNumberICU.cpp
* platform/text/ICULocale.h:
(ICULocale): Add currentLocale().
* platform/text/LocalizedNumberICU.cpp:
(WebCore::convertToLocalizedNumber): Use ICULocale::currentLocale().
(WebCore::convertFromLocalizedNumber): ditto.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@114359 268f45cc-cd09-0410-ab3c-d52691b4dbfc