Support all symbols in definitions

[renkun-ken]

This PR adds all symbols to definitions so that it is easier to search symbols via document/workspace symbol search.

func <- function(x, y) {
  m <- x + y
  n <- x * y
  m + n
}

# R6 class
Person <- R6::R6Class("Person",
  private = list(
    name = NULL,
    age = NULL
  ),
  public = list(
    initialize = function(name) {
      private$name <- name
    },
    greeting = function() {
      cat("Hello, my name is ", private$name, "!\n", sep = "")
    }
))

person <- Person$new(name = "Somebody")

num <- 1
lgl <- TRUE
text <- "hello"

vec <- c(1, 2, 3)

lst <- list(
  x = 1,
  y = 2,
  z = list(a = 1, b = 2)
)

var <- rnorm(100)

The above code has the following symbol outline:

Some function calls are specially treated to generate different kinds of document symbols. c(),matrix(), and array() creates Array symbol, list() creates Struct symbol, and R6Class() creates Class symbol. Code editor or extensions could work with these type-like symbols. In VSCode, for example, git integration could show the git history for Class and Struct symbols.

Also, non-function symbols in global namespace could also have documentation to show in completion.

A screencast: