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Fixes #172899 This PR adds a format_version number to the root table of the 3 flat buffer formats that impellerc creates; runtime stages, shader bundles and shader archives. It also adds a 'format_version' key to the root table of the shader bundle json format for completeness (Though it could be argued that the json format does not require this, I feel it may still be useful there). This allows for format compatibility checks with future versions of the table as @chinmaygarde expressed concerns about in #168294 and @jonahwilliams mentions in #166944 . The current code only checks for compatibility with the current version, but this mechanism allows for backwards compatibility in the future and not handling flat buffers with formats with new version number. The big win here is that format_version numbers allow us to abort parsing anything that we may not understand that could possible cause problems, corruptions or crashes. The changes are simple and straightforward and I feel they lay a reasonable foundation for version handling for any future changes. The version numbers themselves are defined within the `runtime_stage_types.fbs`, `shader_bundle.fbs` and `shader_archive.fbs` where I feel they should be as they can directly be incremented if any changes to the flat buffer format are made. Mechanisms for handling of backwards compatibility in the future should be straightforward to make in the corresponding c++ code allowing for the continued support of older (lower) version numbers if so desired. This addresses #172899 and the other concerns mentioned in the issues/pr's mentioned above. I plan on including my tests for exclusion of non-matching versions - Existing test verify that the version checking confirms matching versions. I wanted to get this out there for discussion before spending more time on this in case this approach is rejected outright. I have a companion PR which adds FragmentProgram.fromBytes() to the engine (c++ and canvaskit/wasm). I wanted to separate the impellerc output versioning into it's own (this) PR. ## Pre-launch Checklist - [X] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [X] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [X] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [X] I signed the [CLA]. - [X] I listed at least one issue that this PR fixes in the description above. - [X] I updated/added relevant documentation (doc comments with `///`). - [FORTHCOMING] I added new tests to check the change I am making, or this PR is [test-exempt]. - [X] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [X] All existing and new tests are passing. --------- Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com> Co-authored-by: gaaclarke <30870216+gaaclarke@users.noreply.github.com> Co-authored-by: Aaron Clarke <aaclarke@google.com>