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.

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tests/threads/tmembug.nim

@@ -12,14 +12,14 @@ var
 chan1.open()
 chan2.open()
 
-proc routeMessage*(msg: BackendMessage) =
+proc routeMessage*(msg: BackendMessage) {.raises: [], gcsafe.} = # no exceptions!
   discard chan2.trySend(msg)
 
 var
   recv: Thread[void]
   stopToken: Atomic[bool]
 
-proc recvMsg() =
+proc recvMsg() {.raises: [], gcsafe.} = # no exceptions!
   while not stopToken.load(moRelaxed):
     let resp = chan1.tryRecv()
     if resp.dataAvailable: