Improved subscript and property access handling

[ballercat]

Normalize and improve property access and subscript in the parser phases.

Fixes, Improvements

Grammar

• Chained subscripts and property access a.b.c.d. Makes working with data-types (like Linked lists) much more stable
• Better handling of subscripts on property access a.b[0] (refactor)

Internal

• fragment renamed to stmt
• stmt is a tagged template literal which allows for "expanding" node objects inside a walt template string, previously this was limited to string literals only.

node; // complex node like a function call or binary expression
return stmt`i32.load(${node} + 1024);`

• Custom generators for memory read/write are removed. This greatly simplifies some optimizations and custom scenarios.

[coveralls]

Pull Request Test Coverage Report for Build 282

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.04%) to 99.629%

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Totals
Change from base Build 273:	-0.04%
Covered Lines:	1950
Relevant Lines:	1950

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💛 - Coveralls