CLDR-18954 Use tags (chits) in ST value input dialog

[btangmu]

-Revise AddValue.vue to support new child component AddValueTags.vue

-Move template to top for consistency with most of our Vue components (we should decide on a consistent convention)

-New radio buttons enable choosing between default Text mode and new Tags mode

-Implement tags with a-tag from Ant Design Vue, see https://www.antdv.com/components/tag

-Display one tag for each Unicode code point; hover shows USV and Unicode name, see https://www.npmjs.com/package/unicode-name

-Enable inserting new tags with [+] buttons that appear between tags, before the first tag, and following the last tag

-Each tag has [x] button for deleting the tag

-Enable inputting a character either directly or by its USV (U+...)

CLDR-18954

• This PR completes the ticket.

ALLOW_MANY_COMMITS=true

[btangmu]

Please note that the ticket is still "investigate", and this PR is intended to illustrate possibilities rather than a final design.

Screenshots are based on running ST locally with these changes.

The input dialog shown above has new "Input mode" radio buttons, and the winning value has just been inserted by clicking the "Winning" button. The path is https://st.unicode.org/cldr-apps/v#/am/Gregorian/471a794c61b793f4 .

After choosing "Tags", hovering on the first tag shows the USV and character name.

After clicking on the leftmost [+], an input box is displayed for inserting a character. The user has typed "A".

After clicking on the rightmost [+], an input box is displayed for inserting a character. The user has typed "U+20000".

After pressing Return or clicking outside the input box, the character 𠀀 is displayed and the hover shows the USV and character name.

Hovering on "Text" or "Tags" shows description of the input mode. Note that a checkbox could be used instead, or there could be more than two modes. For example, sequences of ordinary characters could be combined in one tag, and separate tags could be displayed only for special characters such as thin spaces. Or, text and tags could be displayed simultaneously. Or, additional controls could be displayed for choosing from a palette of special characters to input.

[btangmu]

So far (commits 1 and 2) this PR only supports the conventional U+... notation (plus character names) to help identify characters. A likely enhancement would be to add support for codes like ❰TSP❱ for thin space; see https://cldr.unicode.org/translation/core-data/exemplars#key-to-escapes