Angular renderer does not export `provideMarkdownRenderer` function

[jacobsimionato]

I think https://github.com/google/A2UI/blob/main/renderers/angular/src/v0_9/public-api.ts should export https://github.com/google/A2UI/blob/main/renderers/angular/src/v0_9/core/markdown.ts so that people can use it.

[jacobsimionato]

A minor fix for if you have time, @josemontespg !

[josemontespg]

This is a good idea. Merged in #1189