Resolve merge conflicts with devel branch refactoring (#25423)

The PR branch had merge conflicts with `devel` due to a major compiler
refactoring that extracted type definitions from `compiler/ast.nim` into
a new `compiler/astdef.nim` file.

## Changes

- Resolved conflict in `compiler/ast.nim` by accepting `devel`'s
refactored structure
- Merged 763 commits from `devel` branch (commit range:
`ce6a345..b3273e7`)
- Preserved original PR changes removing deprecated symbols from
`lib/core/macros.nim`

The core PR functionality (removal of deprecated macros API since
v0.18.1) remains intact while incorporating the upstream AST
refactoring.

<!-- START COPILOT CODING AGENT TIPS -->
---

💡 You can make Copilot smarter by setting up custom instructions,
customizing its development environment and configuring Model Context
Protocol (MCP) servers. Learn more [Copilot coding agent
tips](https://gh.io/copilot-coding-agent-tips) in the docs.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: ringabout <43030857+ringabout@users.noreply.github.com>

compiler/plugins/itersgen.nim

@@ -33,7 +33,7 @@ proc iterToProcImpl*(c: PContext, n: PNode): PNode =
 
   let prc = newSym(skProc, n[3].ident, c.idgen, iter.sym.owner, iter.sym.info)
   prc.typ = copyType(iter.sym.typ, c.idgen, prc)
-  excl prc.typ.flags, tfCapturesEnv
+  excl prc.typ, tfCapturesEnv
   prc.typ.n.add newSymNode(getEnvParam(iter.sym))
   prc.typ.rawAddSon t
   let orig = iter.sym.ast