feat(lsp): support workspace/foldingRange/refresh #41780

Problem:
Servers cannot request refreshing stale LSP folding ranges after a
project-wide change.

Solution:
Advertise `workspace.foldingRange.refreshSupport` and re-request folding
ranges for active buffers when handling `workspace/foldingRange/refresh`.

AI-assisted

runtime/lua/vim/lsp/protocol.lua

@@ -639,6 +639,9 @@ function protocol.make_client_capabilities()
       diagnostics = {
         refreshSupport = true,
       },
+      foldingRange = {
+        refreshSupport = true,
+      },
       fileOperations = {
         dynamicRegistration = false,
         didCreate = false,