std.uni: optimize fullCaseTable

[dkorpel]

Reduce table size from 50kb to 25kb by cutting the entry size in half (16 -> 8 bytes), and shave off 12 ms semantic2 time by using plain integers.

[dlang-bot]

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[dkorpel]

std/internal/unicode_tables.d(40:8)[warn]: Public declaration 'FCE' has no documented example.

FCE is package(std), bug in D-scanner?