nixd/Controller: report error on `textDocument/definition` on builtins #3161

Job	Run time
nix-build-develop-gcc (none, release, true)	3m 3s
nix-build-develop-clang (none, release, true)	2m 57s
nix-build-develop-gcc (none, release, false)	3m 10s
nix-build-develop-clang (none, release, false)	2m 51s
nix-build-develop-gcc (none, debug, true)	2m 59s
nix-build-develop-gcc (none, debug, false)	3m 1s
nix-build-develop-clang (none, debug, true)	2m 44s
nix-build-develop-gcc (address, release, true)	4m 41s
nix-build-develop-clang (none, debug, false)	2m 57s
nix-build-develop-gcc (address, release, false)	4m 56s
nix-build-develop-gcc (address, debug, true)	4m 3s
nix-build-develop-gcc (address, debug, false)	4m 1s
nix-build-develop-gcc (undefined, release, true)	4m 15s
nix-build-develop-gcc (undefined, release, false)	4m 10s
nix-build-develop-gcc (undefined, debug, true)	3m 16s
nix-build-develop-gcc (undefined, debug, false)	3m 25s
	56m 29s

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