analyzer: support selective imports and improve module resolution

[wenxuanjun]

Fixed the parser to correctly recognize selective imports (e.g., import foo { Bar }), so "Go to Definition" and highlighting now work for symbols inside the curly braces.

Improved module resolution logic, which fixes issues in nested project structures (e.g., import bar now correctly resolves to foo.modules.bar). It also prioritizes workspace modules over the standard library, fixing cases where some symbols would jump to vlib instead of the local implementation.

Fixed a symbol shadowing bug. Global variables that share a name with their module are now correctly resolved as variables. Explicitly defined local variables named it are now correctly recognized, instead of being forced to be implicit array iterators.

Enabled indexing for the main function so it now appears in the Document Outline and symbol search. Fixed methods defined on Type Aliases were not resolved (e.g., x.bar() where x is a SumType). Restored broken syntax highlighting for the implements keyword. Fixed definition lookup jumping to incorrect global symbols and miss usages in files that imported the module using a shorter path (e.g. import bar but FQN is foo.modules.bar).

Resolves #153, resolves #149, resolves #17, resolves #107, resolves #159, resolves #98, resolves #103, resolves #151, resolves #105.

[spytheman]

Excellent work.
Thanks a lot @wenxuanjun 🙇🏻 .