planner: correct estimated row count for inner plan of index join

[eurekaka]

What problem does this PR solve?

For index join, if inner plan is table scan, i.e, handle is index join key, and if there is selection above table scan, the estimated row count is wrong. This should has no impact on the final plan chosen, but the explain output is confusing, so I fix it.

What is changed and how it works?

Use stats of table scan instead of datasource as the stats of selection.

Check List

Tests

• Unit test: existing UT covers this fix
• Integration test: existing integration test covers this fix

Code changes

N/A

Side effects

N/A

Related changes

• Need to cherry-pick to the release branch

[eurekaka]

/run-all-tests

[alivxxx]

LGTM

[zz-jason]

LGTM

[codecov]

Codecov Report

Merging #10015 into master will increase coverage by 0.001%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##             master     #10015       +/-   ##
===============================================
+ Coverage   77.7034%   77.7044%   +0.001%     
===============================================
  Files           403        403               
  Lines         81878      81873        -5     
===============================================
- Hits          63622      63619        -3     
+ Misses        13558      13557        -1     
+ Partials       4698       4697        -1