Refactor Error Code definitions

[Seelengrab]

This refactors the way error codes are handled, in preparation for making JSONRPC.jl less LSP specific, by hooking into custom error printing provided by an upstream PR. Requires https://github.com/julia-vscode/JSONRPC.jl/pull/70.

[Seelengrab]

There's also these error codes that seem to overlap considerably:

https://github.com/julia-vscode/LanguageServer.jl/blob/e67befb27eb0783a7dcbef11eca8513d15e3a0a5/src/requests/features.jl#L155-L167

This error code is seemingly used for a formatting failure, but the LSP spec says this specific code should not be used:

/**
 * This is the end range of JSON-RPC reserved error codes.
 * It doesn't denote a real error code.
 *
 * @since 3.16.0
 */
export const jsonrpcReservedErrorRangeEnd = -32000;

This should probably be changed to some other error code, but I don't know how that would interact with the extension.

Similarly, this section also defines a new error code for formatting:

https://github.com/julia-vscode/LanguageServer.jl/blob/e67befb27eb0783a7dcbef11eca8513d15e3a0a5/src/requests/features.jl#L207-L217

This doesn't conflict with the spec, but it doesn't match the existing formatting error code used above. This needs a decision on whether they should be merged into one error code, or kept distinct.

[pfitzseb]

Both of those should be -33000 I think. As far as I'm aware no-one is actually checking for the specific error code anyways, FWIW.