adding mcmc_dots and mcmc_dots_by_chain functions

[behramulukir]

This PR adds mcmc_dots and mcmc_dots_by_chain functions which were requested by @avehtari.

These functions are simply an adaptation of the previously implemented ppc_dots function to the MCMC space. As ppc_dots does, these functions require ggdist to be installed, so it checks whether that is installed, and if it is, then it utilises ggdist::stat_dots to create dot plots.

Tasks:

• implement functions
• implement tests
• update documentation

Examples

x <- example_mcmc_draws()
color_scheme_set("brightblue")

mcmc_dots(x)

mcmc_dots(x, quantiles = 80)

mcmc_dots_by_chain(x, regex_pars = "beta")

[jgabry]

Do you know why two of the new visual tests are failing? Maybe you just need to regenerate the snapshots?

══ Failed tests ════════════════════════════════════════════════════════════════
── Failure ('test-mcmc-distributions.R:218:3'): mcmc_dots renders correctly ────
Snapshot of `testcase` has changed.

Backtrace:
    ▆
 1. └─vdiffr::expect_doppelganger("mcmc_dots (default)", p_base) at test-mcmc-distributions.R:218:3
 2.   ├─base::withCallingHandlers(...)
 3.   └─testthat::expect_snapshot_file(...)
── Failure ('test-mcmc-distributions.R:227:3'): mcmc_dots_by_chain renders correctly ──
Snapshot of `testcase` has changed.

Backtrace:
    ▆
 1. └─vdiffr::expect_doppelganger("mcmc_dots_by_chain (default)", p_base) at test-mcmc-distributions.R:227:3
 2.   ├─base::withCallingHandlers(...)
 3.   └─testthat::expect_snapshot_file(...)

[jgabry]

I just regenerated the SVGs and pushed them. Let's see if it passes now.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.64%. Comparing base (d6e83fd) to head (108e6e7).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #402      +/-   ##
==========================================
+ Coverage   98.62%   98.64%   +0.01%     
==========================================
  Files          35       35              
  Lines        5750     5811      +61     
==========================================
+ Hits         5671     5732      +61     
  Misses         79       79              

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[behramulukir]

Sorry that I wasn't able to get back to this soon. In this commit, I attempted to re-run test-mcmc-distributions.R and update the SVGs, but this resulted in all visual tests failing, so I had to revert to the previous commit.

Now with your update, everything looks okay to me, and tests pass as well, so I'll mark this PR as ready.