[NUI] Remove build warning messages in NUI Samples (#4932)

[NUI] Remove build warning messages in NUI Samples  (#4932)

* [NUI] Remove build warning messages in NUI Samples

 - Replace `PreFocusChangeEventArgs` from `FocusChangingEventArgs`.
 - Use `HorizontalAlignment` or `VerticalAlignment` properties
   instead of `LinearAlignment`/
 - Use new Vector2(...) constructor instead of using `X` or `Y` setter.
 - Remove Unreachable code.

Signed-off-by: Seoyeon Kim <seoyeon2.kim@samsung.com>
* [NUI] Remove build warning messages

 - Remove not used variables : `axis` and `degree`.
 - Clean code according to NUI Coding style
 - Use `HorizontalAlignment` or `VerticalAlignment` properties
   instead of `LinearAlignment`.
 - Use `StyleName` property instead of `SetStyleName(string)`.
 - Use `ChildCount` property instead of `GetChildCount()`.
 - Use new Vector2(...) constructor instead of `Width` or `Height` setter.

Signed-off-by: Seoyeon Kim <seoyeon2.kim@samsung.com>
* [NUI] Remove build warning messages part.3

 - Remove not used variables : mClippedImagePropertyIndex,
mLogoTapDetector, FocusEffect.actor, oldPageCount, FrameUpdateCallback.text, etc.
 - Use `HorizontalAlignment` or `VerticalAlignment` properties
  instead of `LinearAlignment`.
 - Use `ChildCount` property instead of `GetChildCount()`.
 - Use new Vector2(...) constructor instead of `Width` or `Height` setter.
 - Clean code according to NUI Coding style

Signed-off-by: Seoyeon Kim <seoyeon2.kim@samsung.com>
Signed-off-by: Seoyeon Kim <seoyeon2.kim@samsung.com>