Flip the default for build_devtools_from_sources

If all tests pass at this point, and we can publish dev releases, we can stop depending on devtools from cipd.

However, need to check developer impact as bumping Flutter all the time might be an annoying expense for most SDK developers.

Locate the build_devtools_from_sources setting and the tests or release entry points that govern dev releases and the CIPD dependency. First verify the current default and test coverage, then assess the impact of repeatedly bumping Flutter for SDK developers. Done means the tests pass, dev releases can be published, and the dependency decision is validated.

Scritto dal modello di indicizzazione a partire dal testo della issue.