Teach etags new interpreters for some languages

Teach etags new interpreters for some languages

* lib-src/etags.c (Erlang_interpreters, Lua_interpreters)
(Prolog_interpreters, Python_interpreters, Ruby_interpreters): New
static variables.
(lang_names): Use them to set interpreters for Erlang, Lua,
Prolog, Python, and Ruby.
(find_entries): Support "/usr/bin/env FOO" form of specifying an
interpreter.

* test/manual/etags/perl-src/htlmify-cystic: Modify the has-bang
line to test the "env FOO" interpreter spec.  (Bug#30075)
* test/manual/etags/ETAGS.good_1:
* test/manual/etags/ETAGS.good_2:
* test/manual/etags/ETAGS.good_3:
* test/manual/etags/ETAGS.good_4:
* test/manual/etags/ETAGS.good_5:
* test/manual/etags/ETAGS.good_6: Adapt to latest changes in test
files.