Fix PHP symbol retrieval: declare missing Intelephense client capabilities

[EarthmanWeb]

Problem

Intelephense's LSP server conditionally enables certain features based
on what the client declares it supports in the initialize request.
Serena's Intelephense client was missing several capability declarations:

• textDocument.documentSymbol (with hierarchicalDocumentSymbolSupport)
• textDocument.references
• textDocument.hover
• workspace.symbol

Without hierarchicalDocumentSymbolSupport: true, Intelephense falls
back to returning flat SymbolInformation[] instead of the nested
DocumentSymbol[] tree. This means symbol retrieval works partially
or not at all — classes and their methods appear as disconnected
root-level symbols with no parent-child relationship.

Additionally, when find_symbol is called with a specific PHP file
path, it iterated all language servers rather than routing to the
correct one, causing PHP files to be rejected by non-PHP servers.

Fix

• intelephense.py: Added missing client capability declarations
  for documentSymbol (with full hierarchicalDocumentSymbolSupport
  and symbolKind range), references, hover, and workspace
  symbol. Also added assertion that the server confirms
  documentSymbolProvider support after initialization.

• symbol.py: When find_symbols is called with a specific file
  path, route to the appropriate language server via
  get_language_server() instead of iterating all servers.

Example

Before:

# Intelephense returned flat SymbolInformation[] — no hierarchy
symbols = get_symbols_overview("src/Controller.php")
# → {"MyController": [], "index": [], "show": []}
# (methods appear at root level, not nested under class)

After:

symbols = get_symbols_overview("src/Controller.php")
# → {"MyController": {"index": {}, "show": {}}}
# (proper hierarchy via DocumentSymbol[])

[opcode81]

If it shall provide the basis for tests (which it probably should), please move this the PHP test repository.
If it shall not provide the basis for tests, delete it.

[EarthmanWeb]

Removed and provided a new sample file and test

[opcode81]

Tests should be added which validate that the changes result in the improvements described.
In particular, we should explicitly inspect the hierarchical structure in tests.

[EarthmanWeb]

Tests should be added which validate that the changes result in the improvements described. In particular, we should explicitly inspect the hierarchical structure in tests.

All 19 PHP tests pass. Summary of what was added:

test/solidlsp/php/test_php_basic.py — 2 new tests:

test_document_symbols_hierarchical_structure — directly validates the hierarchicalDocumentSymbolSupport fix: asserts Dog class has greet, fetch, getBreed, describe as children (not disconnected root-level symbols), and that those methods do NOT appear at root level
test_full_symbol_tree_within_file — validates request_full_symbol_tree(within_relative_path="sample.php") returns the correct class/method hierarchy
test/serena/test_serena_agent.py — 1 new test:

test_find_symbol_within_php_file — validates the symbol.py routing fix: calls find_symbol(name_path_pattern="Dog/greet", relative_path="sample.php") and asserts the symbol is found (would return empty before the fix, as non-PHP servers would reject the file)