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/objects/tobject_default_value.nim

@@ -819,3 +819,18 @@ block:
 
   var t = MyTyp()
   t.thing[""] = ""
+
+
+type
+  Thing = object
+    a: int = 100 # this is fine
+    b = 100 # this is not
+
+proc overloaded[T: SomeSignedInt](x: T) = discard
+proc overloaded[T: SomeUnsignedInt](x: T) = discard
+proc overloaded[T: object](x: T) =
+  for val in fields(x):
+    var v: typeof(val)
+    overloaded(v)
+
+overloaded(Thing())