Update test text to match spec.

[BigBlueHat]

This includes minimal test changes. Some assert error messages were added and a couple test fixtures where removed since they are no longer needed).

Details below:

• Update @context test to use ordered set language.
• Use a single MUST statement for IDs.
• Rename credential ID fixtures for easy findling.
• Remove duplicate fixture/test post consolidation.
• Update requirements text in Types section.
• Remove skipped SHOULD statement.
• Remove proof type tests.
• Add failure messages to some rejections.
• Add TODOs for Conformance section.
• Extract Verifiable Presentations section.
• Update existing VP test to use new text.
• Add pending test for VP id field.
• Add VP type pending test.
• Add pending tests for Enveloped VCs.
• Add VP holder claims pending tests.
• Create sections for subsections of VP tests.
• Move Data Schemas tests up from Advanced.
• Add some assert messages to help debugging.
• Begin updating Advanced section.
• Remove id tests in Refreshing.
• Unskip Refreshing tests.
• Add links to Refreshing section.
• Add links to termsOfUse tests.
• Add link and note to Evidence test.
• Remove skipped ZKP tests.
• Remove remaining two skipped tests.
• Add comments for possible future tests.
• Add .editorconfig.