More helper methods for `TextFont`

## What problem does this solve or what need does it fill?

Many structures in bevy have helper constructor methods, but the TextFont structure is missing quite a few.

## What solution would you like?

I propose, that the `TextFont` recives new constructor methods

Start by locating the `TextFont` definition in the Bevy source and comparing its available constructors with helper methods on analogous structures. Clarify which constructor methods are wanted and their expected defaults before implementation; the issue is complete when the agreed constructors are added and their behavior is covered consistently with the surrounding API.

Written by the indexing model from the issue text.