FU::Util: Add brotli_compress() and use it for FU output compression

Seems to compresses and perform better than libdeflate at level 6, so
certainly worth using.

FU/Util.pm

@@ -13,7 +13,7 @@ our @EXPORT_OK = qw/
     utf8_decode uri_escape uri_unescape
     query_decode query_encode
     httpdate_format httpdate_parse
-    gzip_lib gzip_compress
+    gzip_lib gzip_compress brotli_compress
     fdpass_send fdpass_recv
 /;
 
@@ -401,6 +401,8 @@ I<zlib(-ng)> the level is capped at 9. 6 is typically used as a default.
 
 Throws an error if no suitable library was found.
 
+This function is B<NOT> safe to use from multiple threads!
+
 =back
 
 This module does not currently implement decompression. If you need that, or
@@ -409,6 +411,22 @@ L<Compress::Raw::Zlib> and L<Compress::Zlib> in the core Perl distribution and
 L<Gzip::Deflate> on CPAN.
 
 
+=head2 Brotli Compression
+
+Just a small wrapper around C<libbrotlienc.so>'s one-shot compression
+interface.
+
+=over
+
+=item brotli_compress($level, $data)
+
+Returns a byte string with the brotli-compressed version of C<$data> at the
+given quality C<$level> (between 0 and 11).
+
+Throws an error if C<libbrotlienc.so> could not be found or loaded.
+
+=back
+
 
 =head2 File Descriptor Passing