implements https://github.com/nim-lang/RFCs/issues/258 (#15503)

* implements https://github.com/nim-lang/RFCs/issues/258

* don't be too strict with custom pragma blocks

* cast pragmas: documentation

* added most missing inference query procs to effecttraits.nim

changelog.md

@@ -304,10 +304,13 @@ proc mydiv(a, b): int {.raises: [].} =
 - `system.deepcopy` has to be enabled explicitly for `--gc:arc` and `--gc:orc` via
   `--deepcopy:on`.
 
-- Added a `std/effecttraits` module for introspection of the inferred `.raise` effects.
+- Added a `std/effecttraits` module for introspection of the inferred effects.
   We hope this enables `async` macros that are precise about the possible exceptions that
   can be raised.
 - Added `critbits.toCritBitTree`, similar to `tables.toTable`, creates a new `CritBitTree` with given arguments.
+- The pragma blocks `{.gcsafe.}: ...` and `{.noSideEffect.}: ...` can now also be
+  written as `{.cast(gcsafe).}: ...` and `{.cast(noSideEffect).}: ...`. This is the new
+  preferred way of writing these, emphasizing their unsafe nature.
 
 
 ## Compiler changes