Rename position to index (#1994)

test/intl402/Segmenter/iterator/following.js

test/intl402/Segmenter/iterator/granularity.js

test/intl402/Segmenter/iterator/position.js

test/intl402/Segmenter/iterator/preceding.js

test/intl402/Segmenter/iterator/prototype.js

...Segmenter/prototype/segment/segment-grapheme-following.js

.../Segmenter/prototype/segment/segment-grapheme-iterable.js

...l402/Segmenter/prototype/segment/segment-grapheme-next.js

...Segmenter/prototype/segment/segment-grapheme-preceding.js

test/intl402/Segmenter/prototype/segment/segment-grapheme.js

...402/Segmenter/prototype/segment/segment-line-following.js

...l402/Segmenter/prototype/segment/segment-line-iterable.js

.../intl402/Segmenter/prototype/segment/segment-line-next.js

...402/Segmenter/prototype/segment/segment-line-preceding.js

test/intl402/Segmenter/prototype/segment/segment-line.js

...Segmenter/prototype/segment/segment-sentence-following.js

.../Segmenter/prototype/segment/segment-sentence-iterable.js

...l402/Segmenter/prototype/segment/segment-sentence-next.js

...Segmenter/prototype/segment/segment-sentence-preceding.js

test/intl402/Segmenter/prototype/segment/segment-sentence.js