Vertically align all buttons in the message input bar to the bottom

[kevinaboos]

As reported by @ymote, when many many lines of text are inputted into the message bar's TextInput widget, the height of the widget will grow until it is off-screen. Because the Location and Send buttons are vertically-aligned to the center of the message bar's height, they may also be displayed off-screen.

Since Makepad does not yet have support for internally-scrollable TextInput views, we cannot set a cap on its height just yet.

Instead, a quick/easy fix for this would be to vertically align all elements to the bottom of the message input bar, and then add some bottom margin in order to make it centered with the typical one-line height of the message TextInput.