v: optimization improvements

[felipensp]

This PR tries to identify points to optimize by checking gprof output by:

• Reducing uneeded string__eq calls
• Removing repeated typ.has_flag(.flag) calls
• Reducing array_get calls where @[direct_array_access] can helps
• Reducing alias_eq calls to numeric types (like ast.Type)
• Reducing check for embed by adding is_embed flag to ast.StructDecl and ast.StructInitField

_{Huly®: V_0.6-21157}

[spytheman]

Excellent work.