[M114 Migration] Always set LC_NUMERIC category to 'C' locale

[M114 Migration] Always set LC_NUMERIC category to 'C' locale

WebVTT's float type position was converted to incorrect css property string in
which ',' is used as decimal point when the locale of LC_NUMERIC category is DE.

blink::String::Format() should always use '.' as decimal point when converting
floats to strings regardless of current locale.
This patch always set LC_NUMERIC category to 'C' locale.

Reference: https://review.tizen.org/gerrit/291129

Change-Id: I601e1ba7e56e5649e078acbc968b5f962f449624
Signed-off-by: Pranay Chauhan <pranay.c1@samsung.com>