Added string.replace() and .replaceAll()

[hkubus]

finishes 1 task off of #683

[hkubus]

@microsoft-github-policy-service agree

[hkubus]

Could you add a test with replacing a string with multiple characters?

Added, also found a bug where replaceAll could loop infinitely so fixed that as well.

[pelikhan]

what if searchvalue equals replace value?

[hkubus]

i believe it shouldn't be an issue, that was part of the bug with replaceAll because if replaceValue contained searchValue it would just match against it forever. Now, after replacing a match it only searches for the index after the position of the replacement value so it can't possibly match against the thing it just replaced. Should i add that as a test just in case anyways?

[pelikhan]

What if you replace "" with ""?