Multi-line to carry number of lines instead of boolean

[lorenzwalthert]

Closes #773.

Here is how the current PR would change benchmark results when merged into master:

• cache_applying: 0.03 -> 0.03 (12.6%)
• cache_recording: 1.08 -> 1.09 (1%)
• without_cache: 3.27 -> 3.23 (-1.4%)

With many int replacements:

• cache_applying: 0.03 -> 0.03 (0%)
• cache_recording: 1.19 -> 1.13 (-4.9%)
• without_cache: 3.57 -> 3.51 (-1.7%)

With them reverted:

• cache_applying: 0.03 -> 0.03 (-0.6%)
• cache_recording: 1.12 -> 1.12 (0%)
• without_cache: 3.44 -> 3.41 (-0.8%)

Ok, I think 1% speed gain is not worth changing every subsetting from x[1] to x[1L]. Readability suffers too much.

[codecov-commenter]

Codecov Report

Merging #782 (464e57c) into master (073a3ec) will increase coverage by 0.07%.
The diff coverage is 90.11%.

❗ Current head 464e57c differs from pull request most recent head e69e812. Consider uploading reports for the commit e69e812 to get more accurate results

@@            Coverage Diff             @@
##           master     #782      +/-   ##
==========================================
+ Coverage   90.55%   90.62%   +0.07%     
==========================================
  Files          47       47              
  Lines        2393     2411      +18     
==========================================
+ Hits         2167     2185      +18     
  Misses        226      226              

Impacted Files	Coverage Δ
R/addins.R	15.29% <0.00%> (ø)
R/token-define.R	66.66% <0.00%> (ø)
R/relevel.R	46.15% <41.17%> (ø)
R/io.R	87.75% <50.00%> (ø)
R/utils-navigate-nest.R	80.00% <63.63%> (ø)
R/unindent.R	95.65% <87.50%> (ø)
R/detect-alignment-utils.R	90.47% <89.47%> (ø)
R/communicate.R	92.30% <100.00%> (ø)
R/compat-dplyr.R	85.71% <100.00%> (ø)
R/detect-alignment.R	98.36% <100.00%> (+0.63%)	⬆️
... and 24 more

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