Allow adding prefix for fields with extends tag

[mskrip]

Added new syntax like extends('Prefix') to enable matching all
extended fields as PrefixFieldName.

Close #1270

[codecov-io]

Codecov Report

Merging #1284 into master will increase coverage by 0.06%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1284      +/-   ##
==========================================
+ Coverage   57.37%   57.44%   +0.06%     
==========================================
  Files          44       44              
  Lines        7813     7837      +24     
==========================================
+ Hits         4483     4502      +19     
- Misses       2773     2777       +4     
- Partials      557      558       +1

Impacted Files	Coverage Δ
tag.go	79.31% <100%> (+2.21%)	⬆️
engine.go	61.79% <100%> (+0.21%)	⬆️
rows.go	52.38% <0%> (-3.76%)	⬇️
session_exist.go	62.26% <0%> (-0.7%)	⬇️

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[lunny]

Join Table Alias Name or prefix of the name, which is better?

SELECT <extends_name>.width, <extends_name>.height

instead of

SELECT <extends_name>width, <extends_name>height

[mskrip]

IMO having just prefix is better here since it refers to what the column name of the query result should be changed to, it doesn't have to have anything in common with the table (the prefix I mean).

[mskrip]

Sorry to bother you, but would I be able to get an ETA on this review? This is kind of a blocking change for me.

[lunny]

How to handle SizeClosed *Size xorm:"extends('')"` ?

[mskrip]

Maybe as if there was no argument? So the same as just xorm:"extends" ?

[lunny]

@mskrip I think it's reasonable.

[mskrip]

@lunny Added test for that case

[mskrip]

@lunny ping

[lunny]

@mskrip will do last review tomorrow morning.

[mskrip]

@lunny Okay, thank you

[lunny]

@mskrip Thanks!