Matrix view support API

[LEOYoon-Tsaw]

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Many other IME support a matrix view, with MxN candidates arranged on M rows and N columns.

This is a Frontend layout, but navigations and selection need additional librime support to function. This is because:

1. On the 2nd and further rows, the first candidate in row is not the 1st one as seen from librime's view.
2. Up and down navigation will switch between changing highlight and paging, depending on the location of highlighted candidate.

One solution is to feed additional information to enable librime handle this layout. There are only 4 parameters librime needs to know:

1. Index of 1st candidate in highlighted row
2. Index of last candidate in row
3. Index of candidate right above highlighted one(null if first row)
4. Index of candidate right below highlighted one(null if last row)

Frontend can feed this information whenever it changes/along with every keystroke.

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

This is the minimal API addition I can think of to support matrix view.

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[llity]

不影响长句的使用，增加了便捷性。能自定义展开的行数。谢谢

[LYWH]

不影响长句的使用，增加了便捷性。能自定义展开的行数。谢谢

请问一下候选词行数您是怎样自定义的呀