lsp-treemacs-initialize is missing now

[timcharper]

In commit e66865623ca1fa4a5a7b6f81901dc5ed21a58acc of treemacs-lsp, the function lsp-treemacs-initialize was removed.

It's unclear what this should reference now. Treemacs-lsp has been promoted to stable and it's unclear, at a quick glance of the code, what should be called instead.

lsp-mssql still refers to it, here:

lsp-mssql/lsp-mssql.el

Line 607 in 88319a6

(lsp-treemacs-initialize)