[ASTextNode] Optimize handling of constrained size to almost never recreate NSLayoutManager

[appleguy]

This also fixes three fairly subtle but serious bugs: #1076, #1046 and #1031.

cc @aaronschubert0 - note I ended up tracing a logic flaw to the most recent patch in this area (#1079), which altered the inset handling with the shadower. I'm still glad you put up this change because it did very clearly appear to improve the behavior, but worsened other situations, like the centering case.

@nvh - you'd be the most valuable tester, although I confirmed both types of clipping miscalculations very strategically recreated in your awesome sample app appear fully corrected.

@yxztj - I actually was using your sample app for the majority of the time it took me to carefully understand and adjust this code.

@bsmith11, @timominous, @AttilaTheFun, @nguyenhuy, @1nput0utput, @stowy, @lappp9, @RCacheaux, @samhsiung, @binl, @rcancro - Please join us in testing!

I'm excited that I feel confident working in this part of the codebase; it's probably one of the few scary corners remaining to be confronted. One of the primary needs now is a big expansion in automated performance and logic testing...

The overall code quality and engineering style in the framework, to me, feels awesome. I'm glad to be working on continuing to do industry-first things as a community together!

[aaronschubert0]

Awesome work @appleguy thanks for putting in the effort to make this area of ASDK so solid!

[nvh]

@appleguy Thanks for looking into this! Most of the bugs, especially those with the centering are fixed in my original use cases. With the firstHeadlineIndent there still is a problem with clipping text on a single line. I've updated my test project to display this behaviour.

Should I open a new issue for this?