lsp-rust: report command capabilities (#4529)

Since
rust-lang/rust-analyzer@49184a1
rust-analyzer no longer assumes clients implement all remote commands.

Since it gates the lenses it returns based on the known commands in
the client, it no longer returns many useful ones.

This PR explicitly lists the available commands, as mapped in the code
a few lines above.

clients/lsp-rust.el

@@ -1761,7 +1761,17 @@ https://github.com/rust-lang/rust-analyzer/blob/master/docs/dev/lsp-extensions.m
   :semantic-tokens-faces-overrides `( :discard-default-modifiers t
                                       :modifiers ,(lsp-rust-analyzer--semantic-modifiers))
   :server-id 'rust-analyzer
-  :custom-capabilities `((experimental . ((snippetTextEdit . ,(and lsp-enable-snippet (fboundp 'yas-minor-mode))))))
+  :custom-capabilities `((experimental .
+                                       ((snippetTextEdit . ,(and lsp-enable-snippet (fboundp 'yas-minor-mode)))
+                                        (commands . ((commands .
+                                                               [
+                                                                "rust-analyzer.runSingle"
+                                                                "rust-analyzer.debugSingle"
+                                                                "rust-analyzer.showReferences"
+                                                                ;; "rust-analyzer.gotoLocation"
+                                                                "rust-analyzer.triggerParameterHints"
+                                                                ;; "rust-analyzer.rename"
+                                                                ]))))))
   :download-server-fn (lambda (_client callback error-callback _update?)
                         (lsp-package-ensure 'rust-analyzer callback error-callback))))