ICU-23401 Correctly implement rule LB3, thereby removing a few more states

[eggrobin]

The line.txt rules have rule statuses distinguishing mandatory breaks (status UBRK_LINE_HARD=100) from break opportunities (status UBRK_LINE_SOFT=0).

However, they incorrectly return UBRK_LINE_SOFT at end of text unless the last character is a hard line break, contrary to https://www.unicode.org/reports/tr14/#LB3. This is unlikely to matter to callers, as the start and end of text would most likely be special-cased in any actual implementation, but it results in unnecessary splitting of states.

Correcting the rules to treat eot as a hard break removes four states from the state machine, as it no longer needs to make unnecessary distinctions between eot and LF etc.: eggrobin/unicodetools@496e9a0...cb6c98a

Checklist

• Required: Issue filed: ICU-23401
• Required: The PR title must be prefixed with a JIRA Issue number. Example: "ICU-NNNNN Fix xyz"
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• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable
• Approver: Feel free to merge on my behalf