Embedding Projector: fix t-SNE control when switching projections

[alicialics]

Motivation for features / changes

If projection is switched from t-SNE to UMAP, t-SNE doesn't pause and the framerate would crash (5fps on M1 pro) If projection is switched from t-SNE to PCA/Custom, t-SNE is stopped, so user has to restart t-SNE when switching back.

Technical description of changes

Pause t-SNE when switching away, resume t-SNE when

Screenshots of UI changes

N/A

Detailed steps to verify changes work correctly (as executed by you)

toggle from t-SNE to any other panel and back to t-SNE will resume t-SNE immediately

Alternate designs / implementations considered