Recurse into special constructs to find document symbols

[lionel-]

Addresses posit-dev/positron#8881

We now consistently recurse inside these constructs to collect nested document symbols such as comment sections:

• if-else branches
• loops

The behaviour regarding nested assignments implemented in #859 has been adapted so that { blocks in if-else branches and loops still counts as top-level. This way these assignments are all treated as consistently part of the outline:

x <- 1

if (TRUE) {
  x <- 2
} else {
  x <- 3
}

for (i in xs) {
  x <- 4
}

In addition we also now collect comment sections in parameter lists of function definitions:

x <- function(
  # section ----
  arg
) {
  ...
}

QA Notes

Comment sections and other kinds of document symbols in if-else branches and loops are now part of the outline:

# top ----

if (TRUE) {
  # if ----
  foo <- function() {}
} else {
  # else ----
  foo <- function() {}
}

for (i in xs) {
  # loop ----
  bar <- function() {}
}

Comment sections in parameter lists of function definitions are now included as well. We don't recurse through default arguments though.

x <- function(
  # section ----
  arg = function() {
    # not a section ----
  }
) {
  ...
}