Derive Document language name from languages.toml name key (#3338)

* Derive Document language name from `languages.toml` `name` key

This changes switches from deriving the language name from the
`languages.toml` `scope` key to `name` (`language_id` in the
`LanguageConfiguration` type). For the most part it works to derive the
language name from scope by chopping off `source.` or `rsplit_once` on
`.` but for some languages we have now like html (`text.html.basic`),
it doesn't. This also should be a more accurate fallback for the
`language_id` method which is used in LSP and currently uses the
`rsplit_once` strategy.

Here we expose the language's name as `language_name` on `Document` and
replace ad-hoc calculations of the language name with the new method.

This is most impactful for the `file-type` statusline element which is
using `language_id`.

* Use `Document::language_name` for the `file-type` statusline element

The `file-type` indicator element in the statusline was using
`Document::language_id` which is meant to be used to for telling
Language Servers what language we're using. That works for languages
with `language-server` configurations in `languages.toml` but shows
text otherwise. The new `Document::language_name` method from the
parent commit is a more accurate way to determine the language.

1 files changed, 1 insertions, 4 deletions

diff --git a/helix-term/src/commands/lsp.rs b/helix-term/src/commands/lsp.rs
index 38507e4d..61eed638 100644
--- a/helix-term/src/commands/lsp.rs
+++ b/helix-term/src/commands/lsp.rs
@@ -863,10 +863,7 @@ pub fn signature_help_impl(cx: &mut Context, invoked: SignatureHelpInvoked) {
                 }
             };
             let doc = doc!(editor);
-            let language = doc
-                .language()
-                .and_then(|scope| scope.strip_prefix("source."))
-                .unwrap_or("");
+            let language = doc.language_name().unwrap_or("");
 
             let signature = match response
                 .signatures