Implement statix Linter and Fixer (#3969)

* Add Statix for Linting

Add `statix check` as a linter. Provides a simple set of definition
tests additionally. Variable names specify "check" to allow for later
addition of `statix fix` as a formatter once stream support is added.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Fixup Supported Tools List

I didn't realise there were two separate lists of tools, so add statix
to the other list. Also, remembered "S" comes after "R", and so
re-ordered it.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Fix statix Test File

I refactored the variables for statix to allow for writing a fixer
later, and forgot to update them in the test, so update them now. Also
remove a stray "i", add missing space before checks

Signed-off-by: David Houston <houstdav000@gmail.com>

* Update Output Stream for v0.4.0

statix v0.4.0 provides a breaking change of output stream from stderr to
stdout.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Add statix fix Fixer

Implement statix fix as a fixer for simple Nix antipatterns.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Fix statix Fixer Tests

Fix the statix fixer tests by removing the unnecessary
'read_temporary_file' value from the command, since it simply uses the
default value.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Add statix Handler Test

Add a test for the statix handler per @hsanson's request.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Fix to run only on stdin for linting

Signed-off-by: David Houston <houstdav000@gmail.com>

autoload/ale/fix/registry.vim

@@ -191,6 +191,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['ruby'],
 \       'description': 'Fix ruby files with standardrb --fix',
 \   },
+\   'statix': {
+\       'function': 'ale#fixers#statix#Fix',
+\       'suggested_filetypes': ['nix'],
+\       'description': 'Fix common Nix antipatterns with statix fix',
+\   },
 \   'stylelint': {
 \       'function': 'ale#fixers#stylelint#Fix',
 \       'suggested_filetypes': ['css', 'sass', 'scss', 'sugarss', 'stylus'],