Rename BigInteger div/mul family of functions (#22794)

## Summary of changes
- renames `mul_2exp` to `mul2Exp`, adjusts it's argument names, marks it
as unstable, and updates the documentation for it
- renames `enum round` to `enum roundingMode` and update its
documentation
- renames `divQ` to `div` and update its documentation
- renames `divR` to `rem` and update its documentation
- renames `divQR` to `divRem` and update its documentation
- renames `divexact` to `divExact` and update its documentation
- renames `divQ2Exp` to `div2Exp`, marks it as unstable, and updates the
documentation for it
- renames `divR2Exp` to `rem2Exp`, marks it as unstable, and updates the
documentation for it
- adds `shiftLeft` and `shiftRight`
- Updated tests using the old names
- Removed previously deprecated `divexact(n,d)` `divisible_p`,
`divisible_2exp_p`, `congruent_p`, and `congruent_2exp_p`
- these have been deprecated for some time, removing them now as they
are not used anymore and it allows for cleaner docs
- Removed previously deprecated `div_qr`, `div_r`, `div_q_2exp`, and
`div_r_2exp`
- these have been deprecated for some time, removing them now as they
are not used anymore and it allows for cleaner docs
- I had to leave `div_q` since it is still being used in submitted
benchmarks
- Added a note to `chpldoc.rst` about `:enum:` 

## New tests
- adds `test/unstable/BigInteger/unstableMul2Exp.chpl`
- adds `test/unstable/BigInteger/unstableDiv2Exp.chpl`
- adds `test/deprecated/BigInteger/deprecateDivexact.chpl`
- adds `test/deprecated/BigInteger/deprecateDivFunctions.chpl`
- adds `test/deprecated/BigInteger/deprecateMul_2exp.chpl`
- removes `test/deprecated/BigInteger/deprecateCongruent2expP.chpl`
- removes `test/deprecated/BigInteger/deprecateCongruentP.chpl`
- removes `test/deprecated/BigInteger/deprecateDivexact.chpl`
- removes `test/deprecated/BigInteger/deprecateDivisible2expP.chpl`
- removes `test/deprecated/BigInteger/deprecateDivisibleP.chpl`

## Testing
- [x] paratest with futures
- [x] paratest + gasnet
- [x] built and checked docs

## Future work
- Update Arkouda to use the new `shiftLeft` and `shiftRight`

[Reviewed by @bmcdonald3]


closes #22731
closes #19303
implements some of the changes from #17724
closes Cray/chapel-private#5099

doc/rst/tools/chpldoc/chpldoc.rst

@@ -504,8 +504,9 @@ a matching identifier is found:
 ``:var:``
 ``:param:``
 ``:type:``
+``:enum:``
 
-    Reference a module-level variable, constant, compiler param, or type.
+    Reference a module-level variable, constant, compiler param, type, or enum.
 
 ``:class:``
 ``:record:``