add testutils.assertAll; privateAccess now works with ref | ptr

[timotheecour]

add testutils.assertAll

for now it's in a private test only module (stdtest/testutils)

compared to unittest.check:

• it is usable at CT
• can be used with statements, which reduces boilerplace and increases readability:

doAssert 1+1 == 2
var a = 3
doAssert a == 4

=>

assertAll:
  1+1 == 2
  var a = 3
  a == 4

see tests

privateAccess now works with ref | ptr

see tests

future work

• pending [superseded] add typetraits.typeOrVoid #17761, reuse typeOrVoid instead of re-defining it