Get other.Rraw running again in r-devel

[MichaelChirico]

A few changes here:

• We need to mess with the attach order. Originally tried attach.required=FALSE but that's not present on R 3.5.0.
• {ggplot2} internals have moved around again. I think the intent of those tests is just to ensure print(<ggplot-obj>) works without error, so I refactored the tests to do that more directly.
• A legit bugfix for example() (described below).

Without the update to cedta() we get the telltale cedta() issues from here:

data.table/inst/tests/other.Rraw

Lines 227 to 229 in fae95de

	# example(":=", local=TRUE) triggered cedta==FALSE and then error, #2972
	test(14.1, {example(':=', package='data.table', local=TRUE, echo=FALSE); TRUE})
	test(14.2, {example('CJ', package='data.table', local=TRUE, echo=FALSE); TRUE})

Expected: 
Observed: [ was called on a data.table in an environment that is not data.table-aware (i.e. cedta()), but ':=' was used, implying the owner of this call really intended for data.table methods to be called. See vignette('datatable-importing') for details on properly importing data.table.
Test 14.2 produced 1 errors but expected 0
Expected: 
Observed: could not find function "J"

AIUI this is because of #7162 adding one more item on the call stack during execution of example().

Split off from #7832 as the actual debugging of package code should be done artisinally.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.01%. Comparing base (46d0934) to head (5dde771).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7833   +/-   ##
=======================================
  Coverage   99.01%   99.01%           
=======================================
  Files          88       88           
  Lines       17234    17234           
=======================================
  Hits        17065    17065           
  Misses        169      169           

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[github-actions]

• HEAD=other-attach-order much slower for as.data.table.array improved in #7019
• HEAD=other-attach-order slower P<0.001 for memrecycle regression fixed in #5463
  

Generated via commit 5dde771

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	3 minutes and 3 seconds
Installing different package versions	23 seconds
Running and plotting the test cases	8 minutes and 22 seconds