Use native virtual-text for vim9 (#4281)

Our current virtual text implementation for vim emulates it by abusing
the textprop and popupwin feature from vim 8.2 (for more details see
commit 708e810414).
This implementation sometimes is janky, for example the popups may leak
into other vim windows next to the current window.

Luckily, vim just got native virtual-text support as a proper subtype to
the prop_add() function. By using the 'text' option, the text property
automatically becomes virtual text that is appended to the current line
if col is zero.

Note that the prop_add() method now returns negative IDs for virtual
text properties.

This feature was added in vim 9.0.0067, but it got a lot of bugfixes
which is why we only use this new API if vim has at least version
9.0.0214.
However, there are still some minor bugs with vim's native virtual text,
so we might have to bump the version check again in the future.

Also see #3906.

Now with proper virtual text support for both vim and neovim available,
we can tackle #2962 in the future by simply tracking multiple virt-texts
instead of just the last one.

In the future we might also want to disable our virtual text emulation
support for vim, as it is a total hack, but for now we should keep it
for backwards compatibility.

autoload/ale/virtualtext.vim

@@ -8,14 +8,21 @@ let g:ale_virtualtext_delay = get(g:, 'ale_virtualtext_delay', 10)
 let s:cursor_timer = -1
 let s:last_pos = [0, 0, 0]
 let s:has_virt_text = 0
+let s:emulate_virt = 0
 
 if has('nvim-0.3.2')
     let s:ns_id = nvim_create_namespace('ale')
     let s:has_virt_text = 1
 elseif has('textprop') && has('popupwin')
-    call prop_type_add('ale', {})
-    let s:last_popup = -1
     let s:has_virt_text = 1
+    let s:emulate_virt = !has('patch-9.0.0214')
+
+    if s:emulate_virt
+        call prop_type_add('ale', {})
+        let s:last_virt = -1
+    else
+        let s:last_virt = 1
+    endif
 endif
 
 function! ale#virtualtext#Clear() abort
@@ -28,10 +35,13 @@ function! ale#virtualtext#Clear() abort
     if has('nvim')
         call nvim_buf_clear_highlight(l:buffer, s:ns_id, 0, -1)
     else
-        if s:last_popup != -1
+        if s:emulate_virt && s:last_virt != -1
             call prop_remove({'type': 'ale'})
-            call popup_close(s:last_popup)
-            let s:last_popup = -1
+            call popup_close(s:last_virt)
+            let s:last_virt = -1
+        elseif s:last_virt != 1
+            call prop_remove({'id': s:last_virt})
+            let s:last_virt = 1
         endif
     endif
 endfunction
@@ -48,12 +58,12 @@ function! ale#virtualtext#ShowMessage(message, hl_group) abort
 
     if has('nvim')
         call nvim_buf_set_virtual_text(l:buffer, s:ns_id, l:line-1, [[l:msg, a:hl_group]], {})
-    else
+    elseif s:emulate_virt
         let l:left_pad = col('$')
         call prop_add(l:line, l:left_pad, {
         \ 'type': 'ale',
         \})
-        let s:last_popup = popup_create(l:msg, {
+        let s:last_virt = popup_create(l:msg, {
         \ 'line': -1,
         \ 'padding': [0, 0, 0, 1],
         \ 'mask': [[1, 1, 1, 1]],
@@ -63,6 +73,17 @@ function! ale#virtualtext#ShowMessage(message, hl_group) abort
         \ 'wrap': 0,
         \ 'zindex': 2
         \})
+    else
+        let type = prop_type_get(a:hl_group)
+
+        if type == {}
+            call prop_type_add(a:hl_group, {'highlight': a:hl_group})
+        endif
+
+        let s:last_virt = prop_add(l:line, 0, {
+        \ 'type': a:hl_group,
+        \ 'text': ' ' . l:msg
+        \})
     endif
 endfunction