Add filter to be able to build custom shipping method rate handers.

[matt-h]

Changes proposed in this Pull Request:

Allows other plugins to be able to extend the capabilities to handle shipping method rates.

This adds a woocommerce_gla_handle_shipping_method_to_rates filter to the shipping_method_to_rates function for the unhandled shipping type method so that other plugins can implement handlers for those shipping methods.

[codecov]

Codecov Report

Merging #2052 (5005c0c) into develop (2da9e70) will increase coverage by 0.1%.
Report is 99 commits behind head on develop.
The diff coverage is 17.9%.

Additional details and impacted files

@@             Coverage Diff             @@
##             develop   #2052     +/-   ##
===========================================
+ Coverage       58.2%   58.3%   +0.1%     
+ Complexity      4119    4114      -5     
===========================================
  Files            454     454             
  Lines          17701   17680     -21     
===========================================
+ Hits           10297   10301      +4     
+ Misses          7404    7379     -25     

Flag	Coverage Δ
php-unit-tests	58.3% <17.9%> (+0.1%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
google-listings-and-ads.php	6.4% <0.0%> (ø)
src/Admin/Admin.php	0.0% <0.0%> (ø)
src/ConnectionTest.php	0.0% <ø> (ø)
src/Google/GlobalSiteTag.php	0.0% <0.0%> (ø)
src/Shipping/ZoneMethodsParser.php	98.4% <100.0%> (+0.1%)	⬆️

[puntope]

Thanks for the contribution. Overall looking good for me, just have a question regarding the need of sending the class instance as a parameter.

[matt-h]

@puntope I didn't need it specifically, was just trying err on the side of passing enough data to solve all potential use cases to filters, even if they aren't needed right away.

Feel free to remove that parameter.

[puntope]

@puntope I didn't need it specifically, was just trying err on the side of passing enough data to solve all potential use cases to filters, even if they aren't needed right away.

Yes, I think is better to keep it as simpler as possible.

Feel free to remove that parameter.

You can change it yourself in your side and I can then approve the PR. 👌

[matt-h]

@puntope I have removed it, should be all set.