remove UTF16/UTF32 support, as they will cause confuse

vlib/encoding/iconv/iconv.v

@@ -6,12 +6,20 @@ import os
 // vstring_to_encoding convert V string `str` to `tocode` encoding string
 // tips: use `iconv --list` check for supported encodings
 pub fn vstring_to_encoding(str string, tocode string) ![]u8 {
+	encoding_name := tocode.to_upper()
+	if encoding_name in ['UTF16', 'UTF32', 'UTF-16', 'UTF-32']! {
+		return error('please use UTF16LE/UTF16BE/UTF32LE/UTF32BE instead')
+	}
 	return conv(tocode, 'UTF-8', str.str, str.len)
 }
 
 // encoding_to_vstring converts the given `bytes` using `fromcode` encoding, to a V string (encoded with UTF-8)
 // tips: use `iconv --list` check for supported encodings
 pub fn encoding_to_vstring(bytes []u8, fromcode string) !string {
+	encoding_name := fromcode.to_upper()
+	if encoding_name in ['UTF16', 'UTF32', 'UTF-16', 'UTF-32']! {
+		return error('please use UTF16LE/UTF16BE/UTF32LE/UTF32BE instead')
+	}
 	mut dst := conv('UTF-8', fromcode, bytes.data, bytes.len)!
 	dst << [u8(0)] // Windows: add tail zero, to build a vstring
 	return unsafe { cstring_to_vstring(dst.data) }
@@ -101,6 +109,10 @@ pub fn remove_utf_string_with_bom(src []u8, utf_type string) []u8 {
 // write_file_encoding write_file convert `text` into `encoding` and writes to a file with the given `path`. If `path` already exists, it will be overwritten.
 // For `encoding` in UTF8/UTF16/UTF32, if `bom` is true, then a BOM header will write to the file.
 pub fn write_file_encoding(path string, text string, encoding string, bom bool) ! {
+	encoding_name := encoding.to_upper()
+	if encoding_name in ['UTF16', 'UTF32', 'UTF-16', 'UTF-32']! {
+		return error('please use UTF16LE/UTF16BE/UTF32LE/UTF32BE instead')
+	}
 	encoding_bytes := vstring_to_encoding(text, encoding)!
 	if bom && encoding.to_upper().starts_with('UTF') {
 		encoding_bom_bytes := create_utf_string_with_bom(encoding_bytes, encoding)
@@ -112,6 +124,10 @@ pub fn write_file_encoding(path string, text string, encoding string, bom bool)
 
 // read_file_encoding reads the file in `path` with `encoding` and returns the contents
 pub fn read_file_encoding(path string, encoding string) !string {
+	encoding_name := encoding.to_upper()
+	if encoding_name in ['UTF16', 'UTF32', 'UTF-16', 'UTF-32']! {
+		return error('please use UTF16LE/UTF16BE/UTF32LE/UTF32BE instead')
+	}
 	encoding_bytes := os.read_file_array[u8](path)
 	println(encoding_bytes)
 	encoding_without_bom_bytes := remove_utf_string_with_bom(encoding_bytes, encoding)