Set cypress downloads and videos folders.

[mshima]

Fixes #18536.

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[mraible]

It's OK to specify these folders. However, I'm more interested in ignoring them. Downloads, screenshots, and videos don't seem like something you'd want in source control.

[mshima]

BUILD_DIR is target for maven and build for gradle.
They are ignored by git.
We already put node, webpack cache, cypress screenshots and others temporary directories there.