t/unit-tests: add UTF-8 width tests for CJK chars

t/unit-tests: add UTF-8 width tests for CJK chars

The file "builtin/repo.c" uses utf8_strwidth() to calculate the display
width of UTF-8 characters in a table, but the resulting output is still
misaligned. Add test cases for both utf8_strwidth and utf8_strnwidth to
verify that they correctly compute the display width for UTF-8
characters.

Also updated the build configuration in Makefile and meson.build to
include the new test suite in the build process.

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>