doAssertRaises improvements; nimscript supports except Exception as e

[timotheecour]

• doAssertRaises now correctly handles foreign exceptions
• now shows which exception is raised on mismatch
• now allows to specify that we expect a foreign exception
• nimscript now handles except Exception as e

{.emit:"""
#include <stdexcept>
void fn(){
  throw std::runtime_error("asdf");
}
""".}

proc fn(){.importcpp.}

proc main() =
  # ok
  doAssertRaises(void): fn() # ok
  doAssertRaises(AssertionDefect): doAssert false
  doAssertRaises(Exception): raise newException(Exception, "")
  doAssertRaises(Exception): doAssert false

  # these will raise AssertionDefect
  when false:
    doAssertRaises(Exception): fn() # expected raising 'Exception', instead raised foreign exception by:
    doAssertRaises(CatchableError): fn() # expected raising 'CatchableError', instead raised foreign exception by:
    doAssertRaises(CatchableError): doAssert false # expected raising 'CatchableError', instead raised 'AssertionDefect' by:
    doAssertRaises(void): doAssert false # expected raising 'foreign exception', instead raised 'AssertionDefect' by:

main()

[timotheecour]

@Araq PTAL, see #15765 (comment)

[timotheecour]

PTAL, removed overload from this PR