cString => cSourceString; tyCString => tyCstring so that error msgs show cstring, not cString (#17744)

lib/system/assign.nim

@@ -167,7 +167,7 @@ when false:
     of tyPointer: k = "range"
     of tyOpenArray: k = "openarray"
     of tyString: k = "string"
-    of tyCString: k = "cstring"
+    of tyCstring: k = "cstring"
     of tyInt: k = "int"
     of tyInt32: k = "int32"
     else: k = "other"

lib/system/hti.nim

@@ -40,7 +40,7 @@ type
     tyPointer,
     tyOpenArray,
     tyString,
-    tyCString,
+    tyCstring,
     tyForward,
     tyInt,
     tyInt8,

lib/system/repr.nim

@@ -281,7 +281,7 @@ when not defined(useNimRtl):
     of tyString:
       let sp = cast[ptr string](p)
       reprStrAux(result, sp[].cstring, sp[].len)
-    of tyCString:
+    of tyCstring:
       let cs = cast[ptr cstring](p)[]
       if cs.isNil: add result, "nil"
       else: reprStrAux(result, cs, cs.len)

lib/system/reprjs.nim

@@ -200,7 +200,7 @@ proc reprAux(result: var string, p: pointer, typ: PNimType,
     var fp: int
     {. emit: "`fp` = `p`;\n" .}
     add(result, reprStr(cast[string](p)))
-  of tyCString:
+  of tyCstring:
     var fp: cstring
     {. emit: "`fp` = `p`;\n" .}
     if fp.isNil: