Be consistent about the value of pi

We have a qmath.h that, sensibly enough, does

#ifndef M_PI
#define M_PI (3.14159265358979323846)
#endif

Despite this, 302 other places in my Qt-dev source tree supply their own values for pi. There is some diversity of values. Let's start with the correctly-rounded ones:

• 3.14159
• 3.14159265 (enough for float - see below)
• 3.14159265358979
• 3.141592653589793 (enough for double - see below)
• 3.1415926535897932
• 3.141592653589793238
• 3.14159265358979323846 (same as M_PI in qmath.h)
• 3.1415926535897932384626433832795
• 3.14159265358979323846264338327950288
• 3.14159265358979323846264338327950288419717
• 3.14159265359
• 3.1415927

Then the truncated ones that aren't correct roundings (in each case, the last digit needs +1):

• 3.1415
• 3.141592
• 3.1415926
• 3.1415926535
• 3.141592653589

Finally, the values that look suspiciously like they were meant to be pi, but aren't (inserting a space after the last matching digit):

• 3.1415 2 (missing 9) In several parameters to sin(...)
• 3.14159 62 (last two digits swapped) In some JS benchmarks
• 3.14159265358979 23846 (missing 3) In an ECMA JS test

I am fairly sure the parameters to sin were meant to use pi; and I suspect changing the JS tests is out-of-scope as they look like imports (i.e. third-party).

Some of these are in JS (which can use Math.PI), including some in QML.
The ones in C++ code should surely use M_PI (and #include <qmath.h> to access it).
Some are in shaders, where we can't use either of those, but can at least be consistent about which literal value we use.