Raise syntax error on invalid unicode escape sequences

[matetokodi]

Raise syntax error on invalid unicode escape sequences instead of failing with an assertion

The parser context was required for raising the error, which had to be added to all functions that can call lexer_unchecked_hex_to_character.

This fixes https://github.com/jerryscript-project/jerryscript/issues/5134

[zherczeg]

This patch adds a lot of extra operations. I am thinking why this was not needed before, how we handled this in other cases.