Bug 40436: Use intermediate files for default bridge lines

Closes #40436 (closed).

With this patch the list of bridges can be found in the following files, with one bridge per line:

• projects/common/bridges_list.obfs4.txt
• projects/common/bridges_list.meek-azure.txt
• projects/common/bridges_list.snowflake.txt

/cc @meskio

I did not finish building with this patch yet, so this is still a draft.