Simplify the code for most linters and tests with closures

autoload/ale.vim

@@ -197,6 +197,11 @@ function! ale#Var(buffer, variable_name) abort
     return get(l:vars, l:full_name, g:[l:full_name])
 endfunction
 
+" As above, but curry the arguments so only the buffer number is required.
+function! ale#VarFunc(variable_name) abort
+    return {buf -> ale#Var(buf, a:variable_name)}
+endfunction
+
 " Initialize a variable with a default value, if it isn't already set.
 "
 " Every variable name will be prefixed with 'ale_'.