ast, builder, checker, parser: fix typos

[ttytm]

Fixes some typos. In a recent commit, one of the tests I added had an incorrect name that did not reflect what it does, so the name has been updated here as well.

🤖 Generated by Copilot at e40d334

This pull request fixes various typos and spelling errors in the comments and test files of the vlib/v module, improving the documentation and testing quality. It also moves a function definition to a more appropriate file and adds a new test case for a compiler error.

🤖 Generated by Copilot at e40d334

• Fix typos in comments and variable names (link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link)
• Move Table.find_fn function from vlib/v/ast/table.v to vlib/v/ast/ast.v (link)
• Fix a typo in a variable name in vlib/v/builder/rebuilding.v (link)
• Add a new test output file for a compiler error related to importing a module with the same name as an alias (link)
• Rename a test source file from import_mod_duplicate_as_sub_err.vv to import_mod_duplicate_as_alias_err.vv (link)
• Delete a test output file that is no longer needed (link)