Allow tbl in i to use 'i.' and 'x.' prefixes in joins

[MichaelChirico]

Closes #6998

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.69%. Comparing base (b689cd2) to head (b7fce75).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7025   +/-   ##
=======================================
  Coverage   98.69%   98.69%           
=======================================
  Files          79       79           
  Lines       14676    14676           
=======================================
  Hits        14485    14485           
  Misses        191      191           

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[github-actions]

Generated via commit b7fce75

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

Task	Duration
R setup and installing dependencies	4 minutes and 40 seconds
Installing different package versions	9 minutes and 15 seconds
Running and plotting the test cases	1 minutes and 51 seconds

[tdhock]

cool!
I noticed a similar issue, #5564 which I thought may be fixed by this PR, but I just tested it, and it seems to still not work.

[tdhock]

THanks, I approve but I don't see the approve review button for some reason.