Include all_aconfig_declarations in droid dist

Include all_aconfig_declarations in the droid dist directory
(identically to how it is already included in the sdk dist).

For local builds, `printflags` is still the recommended way to read
all_aconfig_declarations; the dist-ed files are intended as a way to
inspect remote builds, such as CI builds.

Bug: 324281288
Test: lunch aosp_oriole-trunk-eng && m droid dist && test -e out/dist/flags.pb && test -e out/dist/flags.textproto
Change-Id: Ic29d69ab5014593a3f9213f8a5b55e0569922cc9