[Compile Time Constant Extraction] Add extraction of paren expressions

[jPaolantonio]

Add compile-time extraction of ParenExpr.

Supports the following types of extraction:

    static var float2: Float { return (6) }
    static var float3: Float { return (1 + 2) }
    let string2: String = ("Hi")
    var string3: String { ("Hey") }

[jPaolantonio]

@swift-ci test

[artemcm]

Does this handle (("hi"))? i.e. does the compiler automatically convert that to a single paren statement or would we need to recurse?

[jPaolantonio]

Does this handle (("hi"))? i.e. does the compiler automatically convert that to a single paren statement or would we need to recurse?

Let me check + add a test case.

[jPaolantonio]

@artemcm - Updated with nested parens and recursive extraction is working as expected.

[jPaolantonio]

@swift-ci test