Switching to a more "soft" solution which will be focused on apt only.
Apt will now send an application package name (com.termux) and prefix
(/data/data/com.termux/files/usr) as part of user-agent string. That
will allow to distinguish real Termux users from parties which download
our packages and binary-patching them for the custom prefix.
Note that this will disable user's possibility to set custom User-Agent
for apt.
In issue https://github.com/termux/termux-packages/issues/6160 I have found
that community repo "its-pointless.github.io" specifies us as maintainer
for its packages. This is NOT TRUE and potentially misleads people using
these packages.
Now TERMUX_PKG_MAINTAINER will contain a default value which is neutral
and not specify maintainer. So all packages now have to override it to
the correct value.
[skip ci]
%ci:no-build
Add a small stub which verifies whether /data/data/com.termux/files/usr is readable
into few important packages such like Bash or APT. If this check fails, e.g.
in case if binary was executed in program with different package name (non-Termux),
program will print warning and exit with error status immediately.
This should prevent use of prebuilt packages by third-party applications.
NOTE: for now it uses /data/data/com.termux/files/usr in reversed order to
prevent automatic "blind" patching with sed. Will replace with randomized
XOR-based variant in case if that measure won't be enough.
