fix: make ErlangLanguageServer instantiable (implement _create_base_initialize_params)

[ibakard]

Problem

ErlangLanguageServer cannot be instantiated at all. Every Serena tool fails on an Erlang project during project initialisation:

The language server manager is not initialized, indicating a problem during project initialisation.
Failed to start 1 language server(s):
erlang: Can't instantiate abstract class ErlangLanguageServer without an implementation
for abstract method '_create_base_initialize_params'

Because the failure is at initialisation, it takes down every tool, not just the one called — get_symbols_overview, find_symbol, find_referencing_symbols and the editing tools all fail identically.

Cause

When server-specific initialize params were moved behind the abstract _create_base_initialize_params hook on SolidLanguageServer (ls.py), the Erlang backend was not converted with the others. It still builds its initialize dict inline inside _start_server and passes it straight to self.server.send.initialize(...), so it never implements the abstract method and the class is left abstract.

This is not environment-specific: it reproduces with erlang_ls correctly installed and on PATH, on current main.

Fix

Convert the backend to the same pattern the other language servers use (compare ocaml_lsp_server.py):

• Move the capabilities block out of _start_server into _create_base_initialize_params.
• Drop processId / rootPath / rootUri from the literal — DefaultInitializeParamsBuilder supplies those, and the method's docstring explicitly says implementations should not set them.
• Have _start_server build its params via self._create_initialize_params().
• Remove the now-unused pathlib import.

No behavioural change beyond making the class instantiable; the capabilities advertised to erlang_ls are the same ones the inline dict sent. The # type: ignore[arg-type] on the initialize call is no longer needed, since _create_initialize_params() returns a properly typed InitializeParams.

Verification

Against a real rebar3 umbrella project (~12 OTP applications), with erlang_ls on PATH:

• ErlangLanguageServer.__abstractmethods__ is now empty — the class instantiates.
• get_symbols_overview on a 700-line module returns its functions, records and macros.
• find_referencing_symbols on a record returns 26 cross-references with correct locations and snippets.

Note on erlang_ls vs ELP

erlang_ls was archived on 2025-08-15, and #771 tracks moving to ELP; #1149 attempted that and was closed over a branch/CI problem rather than on the merits. This PR takes no position on that migration — it only makes the Erlang backend that currently ships actually usable. If ELP support lands later, this file is likely replaced wholesale, but until then the shipped backend is 100% non-functional and this is a small fix.

[AmirF194]

CONTRIBUTING.md asks for a CHANGELOG.md entry on every PR (under "Submitting Pull Requests"), and every recently merged PR here has one (#1779, #1763, #1759, #1758, #1754). This one doesn't yet; probably belongs under "Language Servers".

The fix itself checks out. _create_base_initialize_params matches the pattern ocaml_lsp_server.py and the other converted backends use, and SolidLanguageServer._create_initialize_params() (ls.py:3193) already supplies processId/rootUri/clientInfo/workspaceFolders through the builder, so dropping them from the literal here is correct rather than a behavior change.

[opcode81]

Thanks for your contribution. It's a shame that ty did not detect this. IDEA does: