Enable multiple-level fold section of R document like RStudio

[Yunuuuu]

Here is some example code to explain this work:

# section one ----
a <- 1:10

## first sub-section ----
b <- letters

### first sub-sub-section ----
d <- 1:2

## second sub-section ----
e <- LETTERS

### sub-sub-section ----
f <- 1:3

#### sub-sub-sub-section ----
g <- 1:20

# complex nested fold section can work well -----
a <- function(x) {b <- function() {
        # collapse following section will not go beyond this function `b`
        # section for function b ------
        x <- 1:2
        x
    }

    # section one ----
    a <- 1:10

    ## first sub-section ----
    b <- letters

    x <- function() {
        # section for function x -----
        c(a, b, d)
    }
}

This is what the outline look like:

[Yunuuuu]

blocks ranges are codes between pairs like ("[" and "]"), ("(" and ")"), and ("{" and "}").

[Yunuuuu]

block_lines_list is a list with two element, the first element is all block start lines and the second is all block end lines

[Yunuuuu]

if there exists some blocks, we firstly extract the outermost blocks (highest_level_block_lines) and treat the content in these blocks as a new R document, so we can re-use this function to parse them.

[renkun-ken]

Thanks for re-submitting the PR. I'll take a look later today.

[renkun-ken]

I re-arranged some functions so that section.R only contains shared functions, and renamed some functions so that they are more consistent with the rest.

[randy3k]

Thank you for working on it!

[renkun-ken]

@Yunuuuu Some of the test cases failed. Would you like to update the test cases in the following files according to the errors reported at https://github.com/REditorSupport/languageserver/runs/7883213618?check_suite_focus=true:

• https://github.com/REditorSupport/languageserver/blob/master/tests/testthat/test-symbol.R
• https://github.com/REditorSupport/languageserver/blob/master/tests/testthat/test-folding.R

[Yunuuuu]

Exclude lines where close brackets stand

[Yunuuuu]

This is what r documents do

[Yunuuuu]

By excluding lines with close brackets, this can be fixed

[Yunuuuu]

Thanks for the reviewing @renkun-ken, I have run R CMD check in my computer which signal no errors

[renkun-ken]

In addition to updating existing test cases, are you interested in adding some new test cases for the newly introduced features in this PR?

[Yunuuuu]

Sorry for the late reply @renkun-ken, I'll improve the test tomorow, it's a little busy these days.

[Yunuuuu]

For symbols, the "Document section symbol works" test in test-symbol.R file has provide nested section symbol test

[Yunuuuu]

Sorry for the delayed test commits, it's busy for the new school semester,

[renkun-ken]

LGTM Thanks for working on this!