feat(lsp)!: vim.lsp.inlay_hint.get(), enable(), is_enabled() #25512

refactor!: `vim.lsp.inlay_hint()` -> `vim.lsp.inlay_hint.enable()`

Problem:
The LSP specification allows inlay hints to include tooltips, clickable
label parts, and code actions; but Neovim provides no API to query for
these.

Solution:
Add minimal viable extension point from which plugins can query for
inlay hints in a range, in order to build functionality on top of.

Possible Next Steps
---

- Add `virt_text_idx` field to `vim.fn.getmousepos()` return value, for
  usage in mappings of `<LeftMouse>`, `<C-LeftMouse>`, etc

runtime/lua/vim/lsp/protocol.lua

@@ -648,7 +648,12 @@ function protocol.make_client_capabilities()
       inlayHint = {
         dynamicRegistration = true,
         resolveSupport = {
-          properties = {},
+          properties = {
+            'textEdits',
+            'tooltip',
+            'location',
+            'command',
+          },
         },
       },
       semanticTokens = {