Use C++20 std::numbers, std::lerp() (#7696)

* use c++20 concepts and numbers for lmms_constants.h

* replace lmms::numbers::sqrt2 with std::numbers::sqrt2

* replace lmms::numbers::e with std::numbers::e
Also replace the only use of lmms::numbers::inv_e with a local constexpr instead

* remove lmms::numbers::pi_half and lmms::numbers::pi_sqr
They were only used in one or two places each

* replace lmms::numbers::pi with std::numbers::pi

* add #include <numbers> to every file touched so far
This is probably not needed for some of these files. I'll remove those later

* Remove lmms::numbers

Rest in peace lmms::numbers::tau, my beloved

* Add missing #include <numbers>

* replace stray use of F_EPSILON with approximatelyEqual()

* make many constants inline constexpr
A lot of the remaining constants in lmms_constants.h are specific to
SaProcessor. If they are only used there, shouldn't they be in SaProcessor.h?

* ok then, it's allowed to be signed

* remove #include "lmms_constants.h" for files that don't need it
- And also move F_EPSILON into lmms_math.h
- And also add an overload for fast_rand() to specify a higher and lower bound
- And a bunch of other nonsense

* ok then, it's allowed to be inferred

* ok then, it can accept an integral

* fix typo

* appease msvc

* appease msvc again

* Replace linearInterpolate with std::lerp()

As well as time travel to undo several foolish decisions and squash tiny
commits together

* Fix msvc constexpr warnings

* Fix msvc float to double truncation warning

* Apply two suggestions from code review

Co-authored-by: Dalton Messmer <messmer.dalton@gmail.com>

* Apply suggestions from code review

Co-authored-by: Dalton Messmer <messmer.dalton@gmail.com>

* fix silly mistake

* Remove SlicerT's dependence on lmms_math.h

* Allow more type inference on fastRand() and fastPow10f()

* Apply suggestions from code review

Co-authored-by: Dalton Messmer <messmer.dalton@gmail.com>

* Clean up fastRand() a little bit more

---------

Co-authored-by: Dalton Messmer <messmer.dalton@gmail.com>

plugins/BitInvader/BitInvader.cpp

@@ -22,7 +22,7 @@
  *
  */
 
-
+#include <cmath>
 #include <QDomElement>
 
 #include "BitInvader.h"
@@ -36,10 +36,9 @@
 #include "NotePlayHandle.h"
 #include "PixmapButton.h"
 #include "Song.h"
-#include "interpolation.h"
+#include "lmms_math.h"
 
 #include "embed.h"
-
 #include "plugin_export.h"
 
 namespace lmms
@@ -121,7 +120,7 @@ sample_t BSynth::nextStringSample( float sample_length )
 	}
 
 	const auto nextIndex = currentIndex < sample_length - 1 ? currentIndex + 1 : 0;
-	return linearInterpolate(sample_shape[currentIndex], sample_shape[nextIndex], fraction(currentRealIndex));
+	return std::lerp(sample_shape[currentIndex], sample_shape[nextIndex], fraction(currentRealIndex));
 }	
 
 /***********************************************************************