Improve audio sharing password handling

This is a backport of ag/31824318.  ag/31424453 against the same bug is
superseded by these changes and need not be backported.

Test: atest
Bug: 389127608
Ignore-AOSP-First: security
Tag: #security
Merged-In: I10c21973340ff4bc8e4f1507b1136890aad43715
Merged-In: I2994fdbfd2aa71970e195bd2989f9abe3246c9cb
Change-Id: If2ad220dc2f4890ee67be62962a9b25d2f803e24