push local variable declarations to their proper scope

[junxzm1990]

Description

The decompiler declares every local variables at the beginning of a function, making them hard to track. This PR pushes the declarations down to the desired scope.

For example,

    fun id2(self: Entity): u64 {
        let _t10;
        let _t9;
        let _t2;
        let _t20;
        let _t1;
        _t1 = &self;
        if ((_t1 is Person) && *&_t1.id > 0) {
            Entity::Person{id: _t20} = self;
            _t2 = _t20
        } else if (_t1 is Institution) {
            Entity::Institution{id: _t9,admin: _t10} = self;
            _t2 = _t9
        } else _t2 = 0;
        _t2
    }

will be optimized into

    fun id2(self: Entity): u64 {
        let _t2;
        let _t1;
        _t1 = &self;
        if ((_t1 is Person) && *&_t1.id > 0) {
            let _t20;
            Entity::Person{id: _t20} = self;
            _t2 = _t20
        } else if (_t1 is Institution) {
            let _t10;
            let _t9;
            Entity::Institution{id: _t9,admin: _t10} = self;
            _t2 = _t9
        } else _t2 = 0;
        _t2
    }

The basic idea: Given a free var, if it is only used in a Sequence, we try to declare the var in this Sequence unless we can do the same thing inside a nested-Sequence.

How Has This Been Tested?

• Existing decompiler test cases.

Type of Change

• New feature
• Bug fix
• Breaking change
• Performance improvement
• Refactoring
• Dependency update
• Documentation update
• Tests

Which Components or Systems Does This Change Impact?

• Validator Node
• Full Node (API, Indexer, etc.)
• Move/Aptos Virtual Machine
• Aptos Framework
• Aptos CLI/SDK
• Developer Infrastructure
• Move Compiler
• Other (Move Decompiler)

[junxzm1990]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• push local variable declarations to their proper scope #17141 👈 (View in Graphite)
• fix decompiler assignment optimization issue #17008 #17120 : 1 other dependent PR (#17140 )
• Fix another control flow structuring bug #17111
• [decompiler] New testing framework and enable recompilation evaluation #17099
• extend control flow optimizations #17086
• main

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