tests: Simplify clear_notes tests ...

This replaces mocking static tests and assumes errors are parsed
through because the actual parser is triggered.

tests: Refactor test_clear_notes to use template_test_*

tests: Document expected parse task

tests: parse: Clarify what error_on_token does

tests: parse: Use a mock class for note skipping

tests: Use static tokens with static locattions

src: Rename syntax to token

parse: Remove SyntaxType ...

Once again I find myself in the pattern of having a useless 'type' value
that just complicates my life. In this case the correct appproach is to
output the AST directly.

parse: Check types when clearing notes, add extra tests

syntax: Refactor draw_syntax_random and add draw_syntax_texttoken ...

I realized draw_syntax_classified is the same as draw_syntax_random, so
just merge them.

Also add draw_syntax_texttoken explicitly meant to weed out cases where
token type is not set.

tests: Clarify function documentation

tests: Refactor clear_notes tests

parse: Handle parent_context in template_parse_invalid

tests: Use one test per invalid case for text and notes

tests: Add template_parse_invalid

tests: Clarify test name in test_clear_notes

parse: Use an error context for clear_notes

src: Pass a parent context to skip_note

parse: Allow attaching a ParseContext to a ParseErrorException

tests: parse: Clean up some includes

tests: parse: Move note tests to their own files