Features.txt: Add string-trimming; replace "#" in feature tags (#1247)

...ng/prototype/endsWith/searchstring-found-with-position.js

...prototype/endsWith/searchstring-found-without-position.js

...tring/prototype/endsWith/searchstring-is-regexp-throws.js

...rototype/endsWith/searchstring-not-found-with-position.js

...otype/endsWith/searchstring-not-found-without-position.js

...uilt-ins/String/prototype/endsWith/this-is-null-throws.js

...ins/String/prototype/endsWith/this-is-undefined-throws.js

...ype/includes/String.prototype.includes_FailBadLocation.js

...totype/includes/String.prototype.includes_FailLocation.js

...e/includes/String.prototype.includes_FailMissingLetter.js

...g/prototype/includes/String.prototype.includes_Success.js

...e/includes/String.prototype.includes_SuccessNoLocation.js

...rototype/includes/String.prototype.includes_lengthProp.js

...s/String/prototype/includes/coerced-values-of-position.js

test/built-ins/String/prototype/includes/includes.js

test/built-ins/String/prototype/includes/length.js

test/built-ins/String/prototype/includes/name.js

...ototype/includes/return-abrupt-from-position-as-symbol.js

.../String/prototype/includes/return-abrupt-from-position.js

...ype/includes/return-abrupt-from-searchstring-as-symbol.js