v.parser: split parser methods to files based on topic

[spytheman]

• parser: extract asm related methods to vlib/v/parser/asm.v
• parser: extract enum related methods to vlib/v/parser/enum.v
• parser: extract module/import related methods to vlib/v/parser/modules_and_imports.v
• parser: extract codegen related methods to vlib/v/parser/codegen.v
• parser: merge modules_and_imports.v to the already existing module.v
• parser: extract message related methods (for producing parse notes/warnings/errors) to vlib/v/parser/messages.v
• parser: extract allowed_lock_prefix_ins from parser.v to vlib/v/parser/asm.v
• parser: extract is_xxxx predicate methods from parser.v to vlib/v/parser/checks.v
• parser: extract attribute related methods from parser.v to vlib/v/parser/attribute.v

[huly-for-github]

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