Add clipboard provider configuration (#8826)

This change adds the `clipboard-provider` setting to the `editor` section
of configuration.

This option can have values of:
- `none` (use an internal buffer)
(on windows only)
- `windows` (use native windows clipboard)
(on MacOS only)
- `macos` (use pbcopy/pbpaste)
(on neiter of the above)
- `wayland`
- `xclip`
- `xsel`
- `win23yank` (for wsl)
(on all targets with "term")
- `termux`
- `tmux`
- `term` (osc codes)
- `custom` (see below for the configuration)

Note for a custom provider the configurations should look like:
```toml
[editor.clipboard-provider.config]
copy = ["tee", "test.txt"]
paste = ["cat", "test.txt"]
primary-copy = ["tee", "test-primary.txt"] // optional
primary-copy = ["cat", "test-primary.txt"] // optional
```

This can be configured at runtime with the usual:
```
set clipboard-provider term
```
Note: I was unable to work out a syntax expression for setting a `custom`
provider at runtime. In my opinion this is probably a fine limitation to
have but I am curious if there is a correct way I couldn't work out.

This ports over the previous provider selection logic so hopefully the
same default behaviour should apply.

I updated the health command to reflect the provider.
Note: this required reading the user configurations within the health command
which warrants discussion as this seems to not have been done before.

This is my first contribution, I am a C++ developer by profession and
a rust hobyist at best so nits and style updates very welcome.

Note: This adds the `nonempty` crate as a new dependency.
This is because I wanted a way to fail parsing custom commands if they
were empty and didn't want to write custom parsign Serde code.
I do not know what the process is for considering new dependencies and
am very willing to change this for an alternative solution when presented
with a better one! I looked for a `serde` annotation as I thought that
was likely but couldn't find one.

helix-term/src/health.rs

@@ -1,10 +1,10 @@
+use crate::config::{Config, ConfigLoadError};
 use crossterm::{
     style::{Color, Print, Stylize},
     tty::IsTty,
 };
 use helix_core::config::{default_lang_config, user_lang_config};
 use helix_loader::grammar::load_runtime_file;
-use helix_view::clipboard::get_clipboard_provider;
 use std::io::Write;
 
 #[derive(Copy, Clone)]
@@ -53,7 +53,6 @@ pub fn general() -> std::io::Result<()> {
     let lang_file = helix_loader::lang_config_file();
     let log_file = helix_loader::log_file();
     let rt_dirs = helix_loader::runtime_dirs();
-    let clipboard_provider = get_clipboard_provider();
 
     if config_file.exists() {
         writeln!(stdout, "Config file: {}", config_file.display())?;
@@ -92,7 +91,6 @@ pub fn general() -> std::io::Result<()> {
             writeln!(stdout, "{}", msg.yellow())?;
         }
     }
-    writeln!(stdout, "Clipboard provider: {}", clipboard_provider.name())?;
 
     Ok(())
 }
@@ -101,8 +99,25 @@ pub fn clipboard() -> std::io::Result<()> {
     let stdout = std::io::stdout();
     let mut stdout = stdout.lock();
 
-    let board = get_clipboard_provider();
-    match board.name().as_ref() {
+    let config = match Config::load_default() {
+        Ok(config) => config,
+        Err(ConfigLoadError::Error(err)) if err.kind() == std::io::ErrorKind::NotFound => {
+            Config::default()
+        }
+        Err(err) => {
+            writeln!(stdout, "{}", "Configuration file malformed".red())?;
+            writeln!(stdout, "{}", err.to_string())?;
+            return Ok(());
+        }
+    };
+
+    match config
+        .editor
+        .clipboard_provider
+        .get_provider()
+        .name()
+        .as_ref()
+    {
         "none" => {
             writeln!(
                 stdout,

helix-view/Cargo.toml

@@ -50,6 +50,7 @@ toml = "0.8"
 log = "~0.4"
 
 parking_lot = "0.12.2"
+nonempty = { version = "0.10.0", features = ["serde", "serialize"] }
 
 
 [target.'cfg(windows)'.dependencies]