Add gpr open/change/close document support & diagnostics

lsp-gpr_documents: edited files document & gpr2 tree handling

lsp-gpr_handlers: add data to allow gpr file parsings & API to
   implements open/change/close document, get symbols requests
   and publish notification

lsp-gpr_files: gpr files (opened & referenced) data structure for
   symbols, navigation, tooltip, completion, etc

lsp-gpr_files-symbols: get symbols implementation

lsp-gpr_file_readers: reader to let parsers access disk & open
   documents

lsp-ada_driver.adb: add server missing references

gpr tests: new get_symbols, get_symbols_hierarchy, publish_diag tests
   update start_stop test

ref eng/ide/ada_language_server#1127

Author: Philippe Gil

source/ada/lsp-ada_driver.adb

@@ -93,7 +93,8 @@ procedure LSP.Ada_Driver is
    Stream      : aliased LSP.Stdio_Streams.Stdio_Stream;
    Ada_Handler : aliased LSP.Ada_Handlers.Message_Handler
      (Server'Access, Server_Trace);
-   GPR_Handler : aliased LSP.GPR_Handlers.Message_Handler;
+   GPR_Handler : aliased LSP.GPR_Handlers.Message_Handler
+     (Server'Access, Server_Trace);
 
    Error_Decorator : aliased LSP.Error_Decorators.Error_Decorator
      (Server_Trace,