Adds support for multiple language servers per language.

Language Servers are now configured in a separate table in `languages.toml`:

```toml
[langauge-server.mylang-lsp]
command = "mylang-lsp"
args = ["--stdio"]
config = { provideFormatter = true }

[language-server.efm-lsp-prettier]
command = "efm-langserver"

[language-server.efm-lsp-prettier.config]
documentFormatting = true
languages = { typescript = [ { formatCommand ="prettier --stdin-filepath ${INPUT}", formatStdin = true } ] }
```

The language server for a language is configured like this (`typescript-language-server` is configured by default):

```toml
[[language]]
name = "typescript"
language-servers = [ { name = "efm-lsp-prettier", only-features = [ "format" ] }, "typescript-language-server" ]
```

or equivalent:

```toml
[[language]]
name = "typescript"
language-servers = [ { name = "typescript-language-server", except-features = [ "format" ] }, "efm-lsp-prettier" ]
```

Each requested LSP feature is priorized in the order of the `language-servers` array.
For example the first `goto-definition` supported language server (in this case `typescript-language-server`) will be taken for the relevant LSP request (command `goto_definition`).

If no `except-features` or `only-features` is given all features for the language server are enabled, as long as the language server supports these. If it doesn't the next language server which supports the feature is tried.

The list of supported features are:

- `format`
- `goto-definition`
- `goto-declaration`
- `goto-type-definition`
- `goto-reference`
- `goto-implementation`
- `signature-help`
- `hover`
- `document-highlight`
- `completion`
- `code-action`
- `workspace-command`
- `document-symbols`
- `workspace-symbols`
- `diagnostics`
- `rename-symbol`
- `inlay-hints`

Another side-effect/difference that comes with this PR, is that only one language server instance is started if different languages use the same language server.

1 files changed, 19 insertions, 8 deletions

diff --git a/helix-term/src/health.rs b/helix-term/src/health.rs
index 480c2c67..031f982c 100644
--- a/helix-term/src/health.rs
+++ b/helix-term/src/health.rs
@@ -2,7 +2,10 @@ use crossterm::{
     style::{Color, Print, Stylize},
     tty::IsTty,
 };
-use helix_core::config::{default_syntax_loader, user_syntax_loader};
+use helix_core::{
+    config::{default_syntax_loader, user_syntax_loader},
+    syntax::LanguageServerFeatureConfiguration,
+};
 use helix_loader::grammar::load_runtime_file;
 use helix_view::clipboard::get_clipboard_provider;
 use std::io::Write;
@@ -192,10 +195,14 @@ pub fn languages_all() -> std::io::Result<()> {
     for lang in &syn_loader_conf.language {
         column(&lang.language_id, Color::Reset);
 
-        let lsp = lang
-            .language_server
-            .as_ref()
-            .map(|lsp| lsp.command.to_string());
+        // TODO multiple language servers (check binary for each supported language server, not just the first)
+
+        let lsp = lang.language_servers.first().and_then(|lsp| {
+            syn_loader_conf
+                .language_server
+                .get(lsp.name())
+                .map(|config| config.command.clone())
+        });
         check_binary(lsp);
 
         let dap = lang.debugger.as_ref().map(|dap| dap.command.to_string());
@@ -264,11 +271,15 @@ pub fn language(lang_str: String) -> std::io::Result<()> {
         }
     };
 
+    // TODO multiple language servers
     probe_protocol(
         "language server",
-        lang.language_server
-            .as_ref()
-            .map(|lsp| lsp.command.to_string()),
+        lang.language_servers.first().and_then(|lsp| {
+            syn_loader_conf
+                .language_server
+                .get(lsp.name())
+                .map(|config| config.command.clone())
+        }),
     )?;
 
     probe_protocol(