This introduces the concept of a language version and pipes it through the various layers of the stack, from aptos CLI down to compiler v2, prover, and transactional test framework.

- The `LanguageVersion` resides in the new file in the Move model, `metadata.rs`. The `CompilerVersion` has been also moved from the package system into there.  Compiler and language version support formatting and parsing. They also support their default being populated from env vars `MOVE_COMPILER_V2` and `MOVE_LANGUAGE_V2`, respectively.
- There is also a new data structure `CompilationMetadata` which we can use to attach to the file format metadata section in subsequent PRs.
- Both compiler and language version have a qualifier whether a particular version is 'stable'. The value of this is populated in `CompilationMetadata` so we can perform run time checks and disallow an unstable version on production chains (subsequent PRs).
- The aptos cli will print out a warning if an unstable compiler or language version is used.
- The language version is attached to the GlobalEnv. The expression builder will refuse to build language constructs not supported by a given language version.
- File format generator will not generate access specifiers if language v2 is not selected or if a special new experiment GEN_ACCESS_SPECIFIERS is on. This mitigates #12623 for now so we can lower priority but does not close it.
- The acquires checks have been adapted to use the language version in the exp_builder instead of the previous flag.
- A new test directory `checking-lang-v1` has been created to contain tests checking for disallowed v2 language features; some acquires related tests have been move there as well.

This introduces the concept of a language version and pipes it through the various layers of the stack, from aptos CLI down to compiler v2, prover, and transactional test framework.

- The `LanguageVersion` resides in the new file in the Move model, `metadata.rs`. The `CompilerVersion` has been also moved from the package system into there.  Compiler and language version support formatting and parsing. They also support their default being populated from env vars `MOVE_COMPILER_V2` and `MOVE_LANGUAGE_V2`, respectively.
- There is also a new data structure `CompilationMetadata` which we can use to attach to the file format metadata section in subsequent PRs.
- Both compiler and language version have a qualifier whether a particular version is 'stable'. The value of this is populated in `CompilationMetadata` so we can perform run time checks and disallow an unstable version on production chains (subsequent PRs).
- The aptos cli will print out a warning if an unstable compiler or language version is used.
- The language version is attached to the GlobalEnv. The expression builder will refuse to build language constructs not supported by a given language version.
- File format generator will not generate access specifiers if language v2 is not selected or if a special new experiment GEN_ACCESS_SPECIFIERS is on. This mitigates #12623 for now so we can lower priority but does not close it.
- The acquires checks have been adapted to use the language version in the exp_builder instead of the previous flag.
- A new test directory `checking-lang-v1` has been created to contain tests checking for disallowed v2 language features; some acquires related tests have been move there as well.

* [compiler-v2] Introduce language version

This introduces the concept of a language version and pipes it through the various layers of the stack, from aptos CLI down to compiler v2, prover, and transactional test framework.

- The `LanguageVersion` resides in the new file in the Move model, `metadata.rs`. The `CompilerVersion` has been also moved from the package system into there.  Compiler and language version support formatting and parsing. They also support their default being populated from env vars `MOVE_COMPILER_V2` and `MOVE_LANGUAGE_V2`, respectively.
- There is also a new data structure `CompilationMetadata` which we can use to attach to the file format metadata section in subsequent PRs.
- Both compiler and language version have a qualifier whether a particular version is 'stable'. The value of this is populated in `CompilationMetadata` so we can perform run time checks and disallow an unstable version on production chains (subsequent PRs).
- The aptos cli will print out a warning if an unstable compiler or language version is used.
- The language version is attached to the GlobalEnv. The expression builder will refuse to build language constructs not supported by a given language version.
- File format generator will not generate access specifiers if language v2 is not selected or if a special new experiment GEN_ACCESS_SPECIFIERS is on. This mitigates #12623 for now so we can lower priority but does not close it.
- The acquires checks have been adapted to use the language version in the exp_builder instead of the previous flag.
- A new test directory `checking-lang-v1` has been created to contain tests checking for disallowed v2 language features; some acquires related tests have been move there as well.

* Addressing reviewer comments