[Avocado] Validate that file paths are not too long

(I didn't propose this. This was proposed by tianxchen-ms from the Shanghai team on Nov 30, 2022; I just converted it from draft)

issues: [Spec PR validation broken for PoliCheck and CredScan jobs because of long path issues · Issue #3825 · Azure/azure-sdk-tools (github.com)](https://github.com/Azure/azure-sdk-tools/issues/3825)

Feedback from wes:

we need to be a start enforcing that teams don't introduce paths that are too long. WE cannot depend on folks having longpath configured correctly on windows as that will be a blocker in a lot of cases.

For reference we have https://github.com/Azure/azure-sdk-tools/blob/main/eng/common/pipelines/templates/steps/verify-path-length.yml which we use in each of our SDK repos to enforce this.

Ruoxuan Wang
[commented Oct 19]

From my perspective, I recommend to implement a validation rule in avocado. The reason is use `verify-path-length.yml` need to build another CI check. Since this function is quite small, so it's unnecessary to build addition check to do that.