[api_summary] Track pubspec.yaml normal package dependencies constraints

[kevmoo]

Currently, api_summary does not inspect pubspec.yaml. Normal dependencies constraints directly impact downstream consumers' resolution space and can introduce breaking changes (or type breaks if exposed).

Example

Changing:

dependencies:
  meta: ^1.10.0

to:

dependencies:
  meta: ^1.11.0

or major version bumps currently produce identical api_summary output.

[lrhn]

Makes sense, but also risks transitivity issues if we use it.

It can track only major version increments of direct dependencies.
Then it won't show if I change from foo: ^3.5.0 to foo: ^3.6.0, but if foo changes a major version dependency in 3.6.0, that matters transitively, and you can't see that from the data in the summaries. You'll have to go to Pub and make a solve, and then you might as well get all the dependency data from there.

It can track every direct dependency in the API summary.
Then you can try to solve dependencies directly on the API summary data.
But then you're reimplementing Pub functionality.

So probably just major version increments of direct dependencies, as a signal, not as something you can use transitively.