add vmutils.debugNimNode, allows using astalgo.debug in user code

[timotheecour]

intended to help investigate compiler issues, which to this day remains difficult and time consuming.

macros.treeRepr is still what should be used for regular users, but treeRepr is a lossy representation, and oftentimes to debug issues you need access to the full PNode fields (recursively), which (currently) is the most faithfully rendered via astalgo.debug which doesn't hide fields (eg flags, comment field etc); this PR allows exposing it in user code so that recompiling the compiler isn't needed (which is time consuming in a multi edit-debug session)

Here's how debugutils relates to vmutils:

• compiler/debugutils.nim: importable from compiler code
• std/vmutils.nim: importable from user code

future work

• improve rendering of debug, eg to render as a tree (like treeRepr) or via an html file with collapsable nodes as shown in std/prettyprints: pretty print any expression (including with cycles), customizable RFCs#385 (I've implemented this in a private branch, it helps a lot debugging issues as it gives a full snapshot of the AST with all the information present)

[timotheecour]

PTAL

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. If you think it is still a valid PR, please rebase it on the latest devel; otherwise it will be closed. Thank you for your contributions.