feat(lsp)!: add vim.lsp.status, client.progress and promote LspProgressUpdate (#23958)

`client.messages` could grow unbounded because the default handler only
added new messages, never removing them.

A user either had to consume the messages by calling
`vim.lsp.util.get_progress_messages` or by manually removing them from
`client.messages.progress`. If they didn't do that, using LSP
effectively leaked memory.

To fix this, this deprecates the `messages` property and instead adds a
`progress` ring buffer that only keeps at most 50 messages. In addition
it deprecates `vim.lsp.util.get_progress_messages` in favour of a new
`vim.lsp.status()` and also promotes the `LspProgressUpdate` user
autocmd to a regular autocmd to allow users to pattern match on the
progress kind.

Also closes https://github.com/neovim/neovim/pull/20327

src/nvim/auevents.lua

@@ -74,6 +74,7 @@ return {
     'LspDetach',              -- after an LSP client detaches from a buffer
     'LspRequest',             -- after an LSP request is started, canceled, or completed
     'LspTokenUpdate',         -- after a visible LSP token is updated
+    'LspProgress',            -- after a LSP progress update
     'MenuPopup',              -- just before popup menu is displayed
     'ModeChanged',            -- after changing the mode
     'OptionSet',              -- after setting any option
@@ -154,6 +155,7 @@ return {
     LspAttach=true,
     LspDetach=true,
     LspRequest=true,
+    LspProgress=true,
     LspTokenUpdate=true,
     RecordingEnter=true,
     RecordingLeave=true,