azp: Stricter if else parser when using unrecognized contextes

[ChristopherHX]

The following passes on dev.azure.com, but fails here due to typo in parammeters

${{ if false }}:
  IsNull: ${{ replace(coalesce(parameters.y, parammeters.y), '''', '''''') }}

The following fails in both parsers

${{ if true }}:
  IsNull: ${{ replace(coalesce(parameters.y, parammeters.y), '''', '''''') }}

[ChristopherHX]

now new bug, the second failure doesn't had a test :(, now it succeeds.

Technically all suppressed errors should be added to a Warnings instance of TemplateValidationErrors, that can be enabled / disabled on demand