Currently the Flutter CLI tool determines a release's version based on git tags. This is not ideal because tags are not immutable, not all fetch workflows also fetch tags, and it has added a lot of complexity to the tool in terms of needing to invoke git sub-commands, which in addition slow down the tool (#111392).

Instead, releases should check in the version and channel data into a JSON file, and the tool should just read this in at runtime.

Related to #91318 and #63106.