Fix token incompatibility for Prism::Translation::Parser::Lexer

This PR fixes token incompatibility for `Prism::Translation::Parser::Lexer`
when using escaped backslash in string literal:

```ruby
"\\ foo \\ bar"
```

## Parser gem (Expected)

```console
$ bundle exec ruby -Ilib -rparser/ruby33 -ve \
'buf = Parser::Source::Buffer.new("example.rb"); buf.source = File.read("example.rb"); p Parser::Ruby33.new.tokenize(buf)'
ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [x86_64-darwin22]
[s(:str, "\\ foo \\ bar"), [], [[:tSTRING, ["\\ foo \\ bar", #<Parser::Source::Range example.rb 0...15>]],
[:tNL, [nil, #<Parser::Source::Range example.rb 15...16>]]]]
```

## `Prism::Translation::Parser` (Actual)

Previously, the tokens returned by the Parser gem were different. The escaped backslash does not match in the `tSTRING` token:

```console
$ bundle exec ruby -Ilib -rprism -rprism/translation/parser33 -ve \
'buf = Parser::Source::Buffer.new("example.rb"); buf.source = File.read("example.rb"); p Prism::Translation::Parser33.new.tokenize(buf)'
ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [x86_64-darwin22]
[s(:str, "\\ foo \\ bar"), [], [[:tSTRING, ["\\\\ foo \\\\ bar", #<Parser::Source::Range example.rb 0...15>]],
[:tNL, [nil, #<Parser::Source::Range example.rb 15...16>]]]]
```

After this correction, the AST and tokens returned by the Parser gem are the same:

```console
$ bundle exec ruby -Ilib -rprism -rprism/translation/parser33 -ve \
'buf = Parser::Source::Buffer.new("example.rb"); buf.source = File.read("example.rb"); p Prism::Translation::Parser33.new.tokenize(buf)'
ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [x86_64-darwin22]
[s(:str, "\\ foo \\ bar"), [], [[:tSTRING, ["\\ foo \\ bar", #<Parser::Source::Range example.rb 0...15>]],
[:tNL, [nil, #<Parser::Source::Range example.rb 15...16>]]]]
```

The reproduction test is based on the following strings.txt and exists:
https://github.com/ruby/prism/blob/v0.24.0/test/prism/fixtures/strings.txt#L79

But, the restoration has not yet been performed due to remaining other issues in strings.txt.

Author: koic

lib/prism/translation/parser/lexer.rb

@@ -284,7 +284,7 @@ def to_a
               elsif ["\"", "'"].include?(value) && (next_token = lexed[index][0]) && next_token.type == :STRING_CONTENT && next_token.value.lines.count <= 1 && (next_next_token = lexed[index + 1][0]) && next_next_token.type == :STRING_END
                 next_location = token.location.join(next_next_token.location)
                 type = :tSTRING
-                value = next_token.value
+                value = next_token.value.gsub("\\\\", "\\")
                 location = Range.new(source_buffer, offset_cache[next_location.start_offset], offset_cache[next_location.end_offset])
                 index += 2
               elsif value.start_with?("<<")