"Shrink"-extent-mode for `Text`

Currently, Textmorphs inside of an Autolayout provide three sizing modes: They can have a fixed extent, hug their content or fill the morph.
We noticed, that there might be a fourth value that one would like to have for Text which we called "shrink":

When setting the width mode of a Text to "shrink", its extent will never grow beyond the extent that would result from "hug", i.e., the morph gets at most exactly as wide as is necessary to display all its text content.
However, the width of the morph would then respond to changes in the width of its container, similar to how it would respond with a width mode of "fill". This would only take effect when the resulting width becomes smaller than the value determined by the "hug" width mode. "Shrink" would also enable text wrapping by default or might even enforce it.

The reason for wanting this are cases where one would like to use the "positioning" capabilities of the layout, for example centering the text morph, while still wanting the fill behavior so that the text morph shrinks when the container is very small to break the text accordingly.

Start by locating the Text morph sizing modes and the Autolayout code that handles fixed, hug, and fill extents. Trace how container-width changes and text wrapping are tested, then define the shrink mode's behavior for both normal and constrained widths before implementing and adding coverage.