[FR] Add support for custom tests in Twig

[rungta]

Twig allows custom test operators to be defined which is leveraged by Craft CMS to include tests like instance of.

Would be great to have support for declaring these as an option similar to twigMultiTags.

Stack Trace

templates/_routers/collective.twig
[error] templates/_routers/collective.twig: Error: ERROR: Unknown test "instance of"
[error]   3 | #}
[error]   4 | 
[error] > 5 | {%- extends (element is instance of ('craft\\elements\\Category') ? [
[error]     |                         ^
[error]   6 |   '_views/collectives/' ~ element.group.handle,
[error]   7 | ] : [
[error]     at TokenStream.error (file:///.../node_modules/@zackad/prettier-plugin-twig/src/melody/melody-parser/TokenStream.js:129:24)
[error]     at Parser.error (file:///.../node_modules/@zackad/prettier-plugin-twig/src/melody/melody-parser/Parser.js:452:21)
[error]     at getTest (file:///.../node_modules/@zackad/prettier-plugin-twig/src/melody/melody-extension-core/operators.js:258:20)
[error]     at Object.parse (file:///.../node_modules/@zackad/prettier-plugin-twig/src/melody/melody-extension-core/operators.js:226:22)
[error]     at Parser.matchExpression (file:///.../node_modules/@zackad/prettier-plugin-twig/src/melody/melody-parser/Parser.js:532:27)
[error]     at Parser.getPrimary (file:///.../node_modules/@zackad/prettier-plugin-twig/src/melody/melody-parser/Parser.js:577:31)