feat(lsp): support textDocument/foldingRange (#31311)

* refactor(shared): extract `vim._list_insert` and `vim._list_remove`

* feat(lsp): add `vim.lsp.foldexpr()`

* docs(lsp): add a todo for state management

* feat(lsp): add `vim.lsp.folding_range.foldclose()`

* feat(lsp): schedule `foldclose()` if the buffer is not up-to-date

* feat(lsp): add `vim.lsp.foldtext()`

* feat(lsp): support multiple folding range providers

* refactor(lsp): expose all folding related functions under `vim.lsp.*`

* perf(lsp): add `lsp.MultiHandler` for do `foldupdate()` only once

runtime/lua/vim/lsp/protocol.lua

@@ -440,6 +440,13 @@ function protocol.make_client_capabilities()
           properties = { 'command' },
         },
       },
+      foldingRange = {
+        dynamicRegistration = false,
+        lineFoldingOnly = true,
+        foldingRange = {
+          collapsedText = true,
+        },
+      },
       formatting = {
         dynamicRegistration = true,
       },