[libc++] Rename operator[].pass.cpp to subscript_operator.pass.cpp (#117216)

This filename includes non FAT32 legal characters, and has caused a few
issues with glob tools that don't escape brackets properly.

GitOrigin-RevId: c7d5ef420d66bf321999a5c922dd6e77f8dc2e9d
diff --git "a/test/std/time/time.cal/time.cal.weekday/time.cal.weekday.members/operator\133\135.pass.cpp" b/test/std/time/time.cal/time.cal.weekday/time.cal.weekday.members/subscript_operator.pass.cpp
similarity index 100%
rename from "test/std/time/time.cal/time.cal.weekday/time.cal.weekday.members/operator\133\135.pass.cpp"
rename to test/std/time/time.cal/time.cal.weekday/time.cal.weekday.members/subscript_operator.pass.cpp