freetype: add support for disabling brotli

[emidoots]

passing enable_brotli=false to freetype
is this possible now, or waiting for more package manager work?

We need to do this:

In theory it can be specified, it's not blocked on any package manager work
in practice, it needs to be specified in multiple places to get it right
harfbuzz depends on freetype, so it needs to be passed in there: https://github.com/hexops/harfbuzz/blob/2c21ab06dd3c5b4fc54000b008b7306296799cb9/build.zig#L35
then the harfbuzz dependency in mach-freetype needs to be updated
then it needs to be specified in both calls to linkFreetype and linkHarfbuzz: https://github.com/hexops/mach-freetype/blob/90b353a9425067010ae5e924dc845e5e5045dab7/build.zig#L66-L84
then your program needs to pass it down as well
so it's hard to get right