Add client and server support to navigate, inspect, reference, and rename block
template and address symbols declared in PSC .def files:
- Client: register language providers for .def (definition, hover, references,
prepare/provide rename) and send the current document text with each request.
- Server: parse .def files into DefDocument/DefDeclaration/DefReference, expose
def-specific LSP endpoints (definition/hover/references/prepareRename/rename),
and integrate .def lookups into existing Tcl hover/definition/references/rename
flows so Tcl calls jump to .def declarations.
- Tcl server keeps a snapshot API for .def documents (current editor content can
replace file on request); only declared names in loaded .def files can be
renamed. Name validation uses DEF_NAME_RE.
Update README and CHANGELOG to document navigation features.
Christoph