CLDR-16606 add alt="ascii" timeformats with plain space for en*; update dtd, DAIP

[pedberg-icu]

CLDR-16606

• This PR completes the ticket.

Add alt="ascii" versions of standard time formats and availableFormats for en[_*] locales; these have ASCII space instead of NNBSP, and clients can choose to use these instead of the regular time formats if these are experiencing problems with apps that parse time formats in a fragile way and cannot handle NNBSP.

Also:

• Update the LDML dtd accordingly (to allow alt="ascii" as needed).
• Update DAIP so that it normalizes spaces to U+0020 for the alt="ascii" forms (instead of normalizing time format spaces to U+202F for Latn, Greek, Cyrl scripts).
• The alt="ascii" forms are intended to have a relatively short life, and they can be mechanically generated from the non-alt forms. Hence they are not included in modern coverage, and do not appear in Survey Tool. Update tests as necessary to reflect this.

[srl295]

should have doc update? (a general issue for alts…)