Implement Constant expressions

[hasithaa]

Tasks.

Constant support the following expressions.

• literal
• list-constructor-expr
• mapping-constructor-expr
• table-constructor-expr
• string-template-expr
• xml-expr
• constant-reference-expr
• type-cast-expr
• unary-expr
• multiplicative-expr
• mod-expr
• additive-expr
• shift-expr
• range-expr
• numerical-comparison-expr
• is-expr
• equality-expr
• binary-bitwise-expr
• logical-expr
• conditional-expr
• ( const-expr )

Module constant declaration is partially implemented

• support [public] const [type-descriptor] identifier = const-expr ;

[rdhananjaya]

I think we also need to support constants of named integer subtypes.
As of swanlake alpha-4 it says constant cannot be defined with type 'int:Signed32', expected a simple basic types or a map of a simple basic type

[prakanth97]

unary-expr is fixed in #30693. Shall update the description?

[gayalkuruppu]

IMO constant expression list-constructor-expr here is a somewhat highly used scenario in coding. Better if we can prioritise that case. WDYT?