[Components] Changed the width of the compose PilotTextField placeholder view to fillMaxWidth

[gbourassa]

The placeholder view used by the PilotTextField is a Text wrapping its width. This was a limitation to get a proper centered textfield.

The proper way to have a centered textfield is to use the text style textAlign. With that field set, the text field text is properly centered, no matter the width of the view

However, it was not possible to get the same behavior for the placeholder, since even when setting its textAlign value, it would still be aligned to the left. The Text content would be centered (but since it wraps its content, it has no effect), but the Text would still be left aligned in its parent.

Setting the placeholder to be as wide as the TextField allows us to have the same behavior for both the actual textField and the placeholder, since they share the same width.

The default behavior remains unchanged, since textAlign default value is start on text styles.