fix: improve a few small things legacy compatibility

[DylanPiercey]

Description

Fixes three small issues:

1. The w-bind migrator would normalize w-bind="./index" to w-bind="./" which was not safe if you had a package.json in the same folder with a main field.
2. widgetConfig was being incorrectly merged into the component instance (as well as being available on this.widgetConfig. This is a regression from perf: optimize serializing renderBody & legacy widgets #1539
3. Previously in Marko 3 template.render with a callback would provide out as the third argument. This has been added back for compatibility.

Checklist:

• I have read the CONTRIBUTING document and have signed (or will sign) the CLA.
• I have updated/added documentation affected by my changes.
• I have added tests to cover my changes.

[codecov]

Codecov Report

Merging #1545 into master will not change coverage by %.
The diff coverage is 75.00%.

@@           Coverage Diff           @@
##           master    #1545   +/-   ##
=======================================
  Coverage   90.53%   90.53%           
=======================================
  Files         356      356           
  Lines       12769    12769           
=======================================
  Hits        11561    11561           
  Misses       1208     1208           

Impacted Files	Coverage Δ
...ges/marko/src/core-tags/migrate/all-tags/w-bind.js	88.37% <50.00%> (ø)
...kages/marko/src/runtime/components/ComponentDef.js	98.73% <100.00%> (ø)
packages/marko/src/runtime/renderable.js	96.77% <100.00%> (ø)

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