separate traditional chinese into big5 and big5-HKSCS

[huyungtang]

encoding/traditionalchinese: separate traditional chinese into big5 and big5-HKSCS

Fixes golang/go#43581

examples:

==================================================
8007 0x5A77 婷 => big5
19240 0x5A77 婷 => big5-HKSCS

==================================================
8616 0x745C 瑜 => big5
19672 0x745C 瑜 => big5-HKSCS

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Message from mzh:

Patch Set 1:

(3 comments)

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Message from Meng Zhuo:

Patch Set 4:

(1 comment)

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Message from Nigel Tao:

Patch Set 4:

(1 comment)

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