Allow filtering fetched or built languages when using --grammar

[kareigu]

Similar to having use-grammars in languages.toml, this PR implements allowing users the filter which grammars are fetched or built by passing a list of languages as a parameter to --grammar fetch or --grammar build.

If no list is provided all available grammars are fetched or built as is current behaviour as well.

Example output

hx --grammar build
Building 143 grammars

hx --grammar build rust cpp
Building 2 grammars

Rationale behind this feature is allowing users to only download the few grammars they might need, without having to mess around with configuration files.

One question arises however with how this should interact with the use-grammars field in languages.toml. With the current implementation settings configured in languages.toml are still honoured, but maybe it would make more sense for those settings to be overridden by the list supplied to the --grammar parameter?