src: do proper StringBytes error handling

- Return `MaybeLocal`s from `StringBytes::Encode`
- Add an `error` out parameter to pass JS exceptions to the callers
  (instead of directly throwing)
- Simplify some of the string generation methods in `string_bytes.cc`
  by unifying the `EXTERN_APEX` logic
- Reduce usage of deprecated V8 APIs.
- Remove error handling logic from JS, the `buffer.*Slice()` methods
  now throw errors themselves.
- Left TODO comments for future semver-major error message
  improvements.

This paves the way for better error messages coming out of the
StringBytes methods.

Ref: https://github.com/nodejs/node/issues/3175
PR-URL: https://github.com/nodejs/node/pull/12765
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

src/string_bytes.h

@@ -105,19 +105,22 @@ class StringBytes {
 
   // Take the bytes in the src, and turn it into a Buffer or String.
   // Don't call with encoding=UCS2.
-  static v8::Local<v8::Value> Encode(v8::Isolate* isolate,
-                                     const char* buf,
-                                     size_t buflen,
-                                     enum encoding encoding);
+  static v8::MaybeLocal<v8::Value> Encode(v8::Isolate* isolate,
+                                          const char* buf,
+                                          size_t buflen,
+                                          enum encoding encoding,
+                                          v8::Local<v8::Value>* error);
 
   // The input buffer should be in host endianness.
-  static v8::Local<v8::Value> Encode(v8::Isolate* isolate,
-                                     const uint16_t* buf,
-                                     size_t buflen);
+  static v8::MaybeLocal<v8::Value> Encode(v8::Isolate* isolate,
+                                          const uint16_t* buf,
+                                          size_t buflen,
+                                          v8::Local<v8::Value>* error);
 
-  static v8::Local<v8::Value> Encode(v8::Isolate* isolate,
-                                     const char* buf,
-                                     enum encoding encoding);
+  static v8::MaybeLocal<v8::Value> Encode(v8::Isolate* isolate,
+                                          const char* buf,
+                                          enum encoding encoding,
+                                          v8::Local<v8::Value>* error);
 
  private:
   static size_t WriteUCS2(char* buf,