Small updates to standard library

[Tjalle-S]

Description
Makes some small additions to the standard library, bringing it more in line with base:

• Re-export id (occasionally useful) and (~) (previously built-in syntax) from Data.Array.Accelerate.
• Add join to Data.Array.Accelerate.Control.Monad.
• Change the Monoid instance for Maybe to require only a Semigroup instance for the element, instead of Monoid.
• Generalize the Eq instance for (sh :. i) to support non-integer shapes. May be useful in combination with slices.
  Add Eq instances for All and Any sh to support this.

How has this been tested?
No additional tests are required. Most of these changes don't change or introduce implementations. The new join functions is a common utility function, with the same implementation as in base.

Types of changes
What types of changes does your code introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

[Tjalle-S]

The change making (~) a standard type operator was introduced only in GHC 9.4.1, meaning the build fails with older versions of GHC. If desirable, backward compatibility could be maintained by conditionally importing and exporting this operator.

[tomsmeding]

9.4.1 is still pretty recent, so yes, a conditional would be appropriate I think.