Adds String.fromCodePoint to the features list (#1606)

features.txt

test/built-ins/String/fromCodePoint/argument-is-Symbol.js

...built-ins/String/fromCodePoint/argument-is-not-integer.js

.../built-ins/String/fromCodePoint/argument-not-coercible.js

test/built-ins/String/fromCodePoint/arguments-is-empty.js

test/built-ins/String/fromCodePoint/fromCodePoint.js

test/built-ins/String/fromCodePoint/length.js

test/built-ins/String/fromCodePoint/name.js

.../built-ins/String/fromCodePoint/number-is-out-of-range.js

test/built-ins/String/fromCodePoint/return-string-value.js

test/built-ins/String/fromCodePoint/to-number-conversions.js