Convert additional sdk_library stub libraries to from stub generation

legacy.i18n.module.platform.api, stable.i18n.module.platform.api and
conscrypt.module.platform.api contributes to api surfaces, but the
corresponding stub libraries were being generated from source during
from-text stub build. This discrepancy may lead to hiddenapi failure.
Thus, enable these modules to be built from txt files during from-text
stub build.

Test: m
Bug: 274805756
Change-Id: I940dc8484b210bb8aea57ead1055983be7cdf5ec