[libc][NFC] rename str_conv_utils to str_to_integer

rename str_conv_utils to str_to_integer to be more
in line with str_to_float.

Reviewed By: sivachandra, lntue

Differential Revision: https://reviews.llvm.org/D113061

GitOrigin-RevId: 31d797f41efe00dbc3eaf5d97778f1c4dd0c15c2
17 files changed