[pub] use 'increase-if-necessary' as the default strategy for pub dependencies

[devoncarew]

• change the default versioning strategy for pub dependencies to increase-if-necessary
• as a side-effect, no longer use the pubspec.yaml 'version' field to try and identify an app vs a package (they'll both get the same default strategy)

I believe this is generally in-line with what's discussed in #4979.

[jeffwidman]

I approved CI to see if any unit tests need updating for this.

Before merging, I want to take one more gander at #4979 and think carefully about the choices there... at first glance, the arguments presented there could just as easily apply to most other ecosystems... not saying it's a bad idea, just that I want to think on it overnight. I'll post in that issue if I have any concerns.

[devoncarew]

Before merging, I want to take one more gander at #4979 and think carefully about the choices there... at first glance, the arguments presented there could just as easily apply to most other ecosystems... not saying it's a bad idea, just that I want to think on it overnight. I'll post in that issue if I have any concerns.

No worries - I'm fine with taking some time to think through the changes (and I'll circle back to this PR to address the test failures).

[mafreud]

@devoncarew, Could you resume fixing the conflicts? I agree with that default versioning strategy for pub is increase-if-necessary.