Unit testing for Array and String

[oovm]

• Passed:

• Array.prototype.join()

• Array.prototype.concat()

• String.prototype.repeat()

• Need fix:

• String.prototype.length

• String.prototype.concat()

[oovm]

Bug: @jasonwilliams

const s = new String('\ud834\udf06');
console.log(s.length)

Should be 2 but return 4.

[oovm]

TODO:

• Format Array display form.

I don't know how to do this.

[oovm]

Bug(known):

const hello = "Hello, ";
hello.concat("world!")

waiting for auto box.

[oovm]

Please review: @jasonwilliams

1. May conflict with Refactor objects #69 , I use a step by step vm in unit testing.

2. CI build failed because of The command "cargo clippy --verbose" exited with 101.

It is caused by the code in #56, I can't modify it.

3. I tried to fix String.prototype.length, but this problem is a bit complicated.

this_str.len() counts UTF8 length, I changed as this_str.chars().count() to count unicode surrogate pair length.

But js string length is UTF16/USC2 length, still different on some special cases.

[jasonwilliams]

@GalAster you looking for me to merge this or you wanting to carry on?

[oovm]

@jasonwilliams It's ready to merge, I'll do the rest after Array format complete.