Native handling of \overline, \widehat, etc.

[topological-modular-forms]

Jim Belk wrote:

If it's possible to make \overline align well with characters, that would be helpful. The default overline alignment is very poor, e.g.
$$\overline{f},\quad \overline{j}, \quad\overline{s}, \quad\overline{A}, \quad\overline{B}, \quad\overline{V}$$
Using \bar only fixes some of these, doesn't match the look of \overline, and has its own problems with some other letters:
$$\bar{f},\quad \bar{j},\quad \bar{s},\quad \bar{A}, \quad\bar{B},\quad \bar{V}, \quad \bar{d}, \quad \bar{m}, \quad \bar{M}, \quad \bar{T}$$
There are similar issues with \widehat. All of this can be fixed with well-chosen \mkern's, but it should be automatic.

Be sure to design and implement this.