feat(treesitter): add @injection.filename

Problem: Injecting languages for file redirects (e.g., in bash) is not
possible.

Solution: Add `@injection.filename` capture that is piped through
`vim.filetype.match({ filename = node_text })`; the resulting filetype
(if not `nil`) is then resolved as a language (either directly or
through the list maintained via `vim.treesitter.language.register()`).

Note: `@injection.filename` is a non-standard capture introduced by
Helix; having two editors implement it makes it likely to be upstreamed.

runtime/doc/news.txt

@@ -240,6 +240,9 @@ The following new APIs and features were added.
     language aliases (e.g., filetype or custom shorthands) registered via
     |vim.treesitter.language.register()| and/or attempt lower case variants of
     the text.
+  • `@injection.filename` will try to match the node text via
+    |vim.filetype.match()| and treat the result as a language name in the same
+    way as `@injection.language`.
   • The `#set!` directive now supports `injection.self` and `injection.parent`
     for injecting either the current node's language or the parent
     |LanguageTree|'s language, respectively.

runtime/doc/treesitter.txt

@@ -654,6 +654,10 @@ parent tree. The language injection query allows you to specify these
     • `@injection.language` - indicates that the captured node’s text may
       contain the name of a language that should be used to re-parse the
       `@injection.content`.
+    • `@injection.filename` - indicates that the captured node’s text may
+      contain a filename; the corresponding filetype is then looked-up up via
+      |vim.filetype.match()| and treated as the name of a language that should
+      be used to re-parse the `@injection.content`.
 
 The language injection behavior can also be configured by some properties
 associated with patterns:

runtime/lua/vim/treesitter/languagetree.lua

@@ -809,6 +809,10 @@ function LanguageTree:_get_injection(match, metadata)
       if name == 'injection.language' then
         local text = vim.treesitter.get_node_text(node, self._source, { metadata = metadata[id] })
         lang = resolve_lang(text)
+      elseif name == 'injection.filename' then
+        local text = vim.treesitter.get_node_text(node, self._source, { metadata = metadata[id] })
+        local ft = vim.filetype.match({ filename = text })
+        lang = ft and resolve_lang(ft)
       elseif name == 'injection.content' then
         ranges = get_node_ranges(node, self._source, metadata[id], include_children)
       end