AstGen: use 'shadows' instead of 'redeclaration' when names are in different scopes

Closes ziglang#8532

Author: Vexu

compile_errors/decl_shadows_local.zig

@@ -16,7 +16,7 @@ fn bar(a: usize) void {
 // backend=stage2
 // target=native
 //
-// :3:15: error: redeclaration of function parameter 'a'
+// :3:15: error: declaration 'a' shadows function parameter from outer scope
 // :1:8: note: previous declaration here
-// :9:19: error: redeclaration of function parameter 'a'
+// :9:19: error: declaration 'a' shadows function parameter from outer scope
 // :6:8: note: previous declaration here

compile_errors/local_shadows_global_that_occurs_later.zig

@@ -8,5 +8,5 @@ fn foo() void {}
 // backend=stage2
 // target=native
 //
-// :2:9: error: local shadows declaration of 'foo'
+// :2:9: error: local variable shadows declaration of 'foo'
 // :5:1: note: declared here

compile_errors/local_variable_redeclares_parameter.zig

@@ -7,5 +7,5 @@ export fn entry() void { f(1); }
 // backend=stage2
 // target=native
 //
-// :2:11: error: redeclaration of function parameter 'a'
+// :2:11: error: local constant 'a' shadows function parameter from outer scope
 // :1:6: note: previous declaration here

compile_errors/local_variable_shadowing_global.zig

@@ -10,5 +10,5 @@ export fn entry() void {
 // backend=stage2
 // target=native
 //
-// :5:9: error: local shadows declaration of 'Bar'
+// :5:9: error: local variable shadows declaration of 'Bar'
 // :2:1: note: declared here

compile_errors/parameter_shadowing_global.zig

@@ -8,5 +8,5 @@ export fn entry() void {
 // backend=stage2
 // target=native
 //
-// :2:6: error: local shadows declaration of 'Foo'
+// :2:6: error: function parameter shadows declaration of 'Foo'
 // :1:1: note: declared here

function_redeclaration.zig

@@ -10,5 +10,5 @@ fn foo() void {
 //
 // :3:1: error: redeclaration of 'entry'
 // :2:1: note: other declaration here
-// :6:9: error: local shadows declaration of 'foo'
+// :6:9: error: local variable shadows declaration of 'foo'
 // :5:1: note: declared here

variable_shadowing.1.zig

@@ -5,5 +5,5 @@ pub fn main() void {
 
 // error
 //
-// :3:9: error: local shadows declaration of 'testing'
+// :3:9: error: local variable shadows declaration of 'testing'
 // :1:1: note: declared here

variable_shadowing.3.zig

@@ -6,5 +6,5 @@ pub fn main() void {
 
 // error
 //
-// :3:19: error: redeclaration of local variable 'i'
+// :3:19: error: loop index capture 'i' shadows local variable from outer scope
 // :2:9: note: previous declaration here

variable_shadowing.4.zig

@@ -6,5 +6,5 @@ pub fn main() void {
 
 // error
 //
-// :3:16: error: redeclaration of local variable 'i'
+// :3:16: error: capture 'i' shadows local variable from outer scope
 // :2:9: note: previous declaration here

variable_shadowing.5.zig

@@ -6,5 +6,5 @@ pub fn main() void {
 
 // error
 //
-// :3:18: error: redeclaration of local variable 'i'
+// :3:18: error: capture 'i' shadows local variable from outer scope
 // :2:9: note: previous declaration here

variable_shadowing.6.zig

@@ -9,5 +9,5 @@ pub fn main() void {
 
 // error
 //
-// :5:13: error: redeclaration of local variable 'i'
+// :5:13: error: capture 'i' shadows local variable from outer scope
 // :2:9: note: previous declaration here

variable_shadowing.7.zig

@@ -5,5 +5,5 @@ pub fn main() void {
 
 // error
 //
-// :3:16: error: redeclaration of local variable 'i'
+// :3:16: error: capture 'i' shadows local variable from outer scope
 // :2:9: note: previous declaration here

variable_shadowing.8.zig

@@ -5,5 +5,5 @@ pub fn main() void {
 
 // error
 //
-// :3:16: error: redeclaration of local variable 'i'
+// :3:16: error: capture 'i' shadows local variable from outer scope
 // :2:9: note: previous declaration here

variable_shadowing.9.zig

@@ -5,5 +5,5 @@ pub fn main() void {
 
 // error
 //
-// :3:28: error: redeclaration of local variable 'i'
+// :3:28: error: capture 'i' shadows local variable from outer scope
 // :2:9: note: previous declaration here