adding EditorConfig with code conventions

.editorconfig

@@ -0,0 +1,58 @@
+# core settings
+# https://editorconfig.org
+
+root = true
+
+[*.cs]
+indent_style = tab
+indent_size = 4
+trim_trailing_whitespace = true
+
+# VS/.NET extensions
+# https://docs.microsoft.com/en-us/visualstudio/ide/editorconfig-code-style-settings-reference
+
+# language style
+dotnet_style_predefined_type_for_locals_parameters_members = true
+dotnet_style_predefined_type_for_member_access = true
+dotnet_style_require_accessibility_modifiers = always
+dotnet_style_readonly_field = true
+dotnet_style_prefer_auto_properties = true
+dotnet_style_prefer_conditional_expression_over_assignment = true
+dotnet_style_prefer_conditional_expression_over_return = true
+dotnet_style_coalesce_expression = true
+dotnet_style_null_propagation = true
+csharp_style_var_for_built_in_types = true
+csharp_style_var_when_type_is_apparent = true
+csharp_style_var_elsewhere = true
+csharp_style_expression_bodied_methods = true
+csharp_style_expression_bodied_properties = true
+csharp_style_expression_bodied_indexers = true
+csharp_style_expression_bodied_accessors = true
+csharp_style_pattern_matching_over_is_with_cast_check = true
+csharp_style_pattern_matching_over_as_with_null_check = true
+csharp_style_inlined_variable_declaration = true
+csharp_prefer_simple_default_expression = true
+csharp_style_pattern_local_over_anonymous_function = true
+csharp_style_conditional_delegate_call = true
+csharp_prefer_braces = false
+dotnet_sort_system_directives_first = true
+dotnet_separate_import_directive_groups = false
+
+# formatting
+csharp_new_line_before_open_brace = types
+csharp_new_line_before_else = true
+csharp_new_line_before_catch = true
+csharp_new_line_before_finally = true
+csharp_indent_case_contents = true
+csharp_indent_switch_labels = true
+csharp_space_after_cast = false
+csharp_space_after_keywords_in_control_flow_statements = true
+csharp_space_between_method_declaration_parameter_list_parentheses = false
+csharp_space_between_method_call_parameter_list_parentheses = false
+csharp_space_before_colon_in_inheritance_clause = true
+csharp_space_after_colon_in_inheritance_clause = true
+csharp_space_around_binary_operators = before_and_after
+csharp_space_between_method_declaration_empty_parameter_list_parentheses = false
+csharp_space_between_method_call_name_and_opening_parenthesis = false
+csharp_space_between_method_call_empty_parameter_list_parentheses = false
+csharp_preserve_single_line_blocks = true