better procvar ambiguity errors, clean up after #20457 (#20932)

* better procvar ambiguity errors, clean up after #20457

fixes #6359, fixes #13849

* only trigger on closedsymchoice again

* new approach

* add manual entry for ambiguous enums too

* add indent [skip ci]

* move to proc

tests/ambsym/tambprocvar.nim

@@ -0,0 +1,19 @@
+discard """
+  action: reject
+  cmd: "nim check $file"
+  nimout: '''
+tambprocvar.nim(15, 11) Error: ambiguous identifier 'foo' -- use one of the following:
+  tambprocvar.foo: proc (x: int){.noSideEffect, gcsafe.}
+  tambprocvar.foo: proc (x: float){.noSideEffect, gcsafe.}
+'''
+"""
+
+block:
+  proc foo(x: int) = discard
+  proc foo(x: float) = discard
+
+  let x = foo
+
+block:
+  let x = `+` #[tt.Error
+          ^ ambiguous identifier '+' -- use one of the following:]#