Subscripts on structs

[ballercat]

This patch allows for subscripts to be applied on struct fields. Currently, it's not possible to do so without assigning the field to another(array) variable.

type Struct = { length: i32, list: i32[] };

...

const struct: Struct = ...;
struct.list[0] = 42; // this is now supported

[coveralls]

Pull Request Test Coverage Report for Build 207

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.005%) to 99.62%

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Totals
Change from base Build 204:	0.005%
Covered Lines:	1919
Relevant Lines:	1919

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💛 - Coveralls