[Rafael-SOWNet]

Fixes #2244.

For about one real argument past 1 in ten, arcsin and arccos evaluated to NaN: arcsin(6 + pi), arccos(6 + pi) and arcsin(1 + sqrt(3)) among them. Of arcsin(k + c) for k from 1 to 40 and c in pi, e, sqrt(2), sqrt(3) and ln(3), 20 of the 200 were NaN, on 2.6.0 as on master. The value exists: sign(x) pi/2 - i arccosh|x|.

Number.Arcsin and Number.Arccos share ArcSinCosInner. For w = x + iy it takes beta = (|w + 1| - |w - 1|) / 2, then arcsin(beta) or arccos(beta). By the triangle inequality, beta is in [-1, 1], and for a real x past 1 it is exactly 1. The two square roots are rounded, though, and for some x the difference comes out a little past 1, where the decimal arcsine is NaN.

beta is now clamped to [-1, 1]. That restores a bound the rounding broke, and changes no value it did not.

	2.6.0 and master	now
"arcsin(6 + pi)".ToEntity().Evaled	NaN	1.5707963267948966 - 2.902976737696685i
"arccos(6 + pi)".ToEntity().Evaled	NaN	2.902976737696685i

Tests: ArcsineOfARealPastOneTest takes arcsin and arccos at plus and minus (k + c) for those 200 arguments. It compares them with the library's convention, measured at 9.14 and -9.14: sign(x) pi/2 - i arccosh|x|, and 0 or pi plus i arccosh|x|. All five constants' cases fail on master. Full suite 18161/0, interactive trio, AOT smoke 73/0, all frameworks build.

Found by work/compilesweep: the compiled arcsin(arcsin(x + pi)) at 6 had a value, and evaluation had none.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.71%. Comparing base (bd750c4) to head (448d773).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2245      +/-   ##
==========================================
- Coverage   86.71%   86.71%   -0.01%     
==========================================
  Files         310      310              
  Lines       67785    67790       +5     
  Branches    19664    19666       +2     
==========================================
+ Hits        58781    58783       +2     
- Misses       4892     4894       +2     
- Partials     4112     4113       +1     

Flag	Coverage Δ
cpp	37.77% <ø> (ø)
csharp	87.26% <100.00%> (-0.01%)	⬇️
fsharp	32.97% <ø> (ø)
interactive	40.72% <ø> (ø)

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Files with missing lines	Coverage Δ
...uriMath/Core/Entity/Continuous/Number/Operators.cs	90.75% <100.00%> (+0.10%)	⬆️

... and 5 files with indirect coverage changes

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