fixes #20811; Nested proc with inner being generic cannot access parameters of outer proc (#25837)

fixes  #20811

This pull request addresses issues with parameter capture in nested
generic procedures and templates, ensuring that outer parameters are
correctly visible and accessible within nested scopes. The main changes
include a fix in the semantic analysis logic and the addition of
targeted regression tests.

### Semantic analysis improvements:
* Updated `semGenericStmtSymbol` in `compiler/semgnrc.nim` to ensure
that parameters from outer scopes are preserved and accessible in nested
generic procedures, fixing visibility issues with captured parameters.

### Added regression tests:
* Added `tests/generics/t20811.nim` to verify that both generic and
plain inner procedures can access parameters from their enclosing
procedure.
* Extended `tests/template/topensym.nim` with a new block for issue
#20811 to test that template-injected parameters are correctly captured
and visible in nested generic procedures.

compiler/semgnrc.nim

@@ -129,7 +129,14 @@ proc semGenericStmtSymbol(c: PContext, n: PNode, s: PSym,
           result.typ = nil
     onUse(n.info, s)
   of skParam:
-    result = n
+    if s.owner == c.p.owner:
+      # Parameters of the routine currently being semchecked stay as local
+      # identifiers
+      result = n
+    else:
+      # Preserve captured outer parameters so nested generic procs can still
+      # see them after the generic pre-pass.
+      result = newSymNode(s, n.info)
     onUse(n.info, s)
   of skType:
     if (s.typ != nil) and

tests/generics/t20811.nim

@@ -0,0 +1,16 @@
+discard """
+  output: '''42
+42'''
+"""
+
+proc outer(j: int) =
+  proc genericInner[T](): int =
+    j
+
+  proc plainInner(): int =
+    j
+
+  echo genericInner[int]()
+  echo plainInner()
+
+outer(42)

tests/template/topensym.nim

@@ -135,6 +135,19 @@ block: # issue #22605 for templates, original complex example
 
   doAssert g2(int) == "error"
 
+block: # issue #20811
+  template injectError(body: untyped): untyped =
+    template error: untyped {.used, inject.} = "injected"
+    body
+
+  proc outerOpen(error: string): string =
+    injectError:
+      proc genericInner[T](): string =
+        error
+      genericInner[int]()
+
+  doAssert outerOpen("captured") == "injected"
+
 block: # issue #23865 for templates
   type Xxx = enum
     error