Allow grouped tooltips for plots with multiple univariate geoms

[IKupriyanov-HORIS]

import numpy as np
import pandas as pd
from lets_plot import *
LetsPlot.setup_html()

np.random.seed(42)
n = 80
x1 = np.linspace(0, 10, n)
y1 = 1.0 + 0.7 * x1 + np.random.normal(scale=1.8, size=n)
df1 = pd.DataFrame({"x": x1, "y": y1})

x2 = np.linspace(0, 10, n)
y2 = 18.0 - 0.4 * x2 + np.random.normal(scale=2.0, size=n)
df2 = pd.DataFrame({"x": x2, "y": y2})

ggplot() + \
    geom_point(data=df1, mapping=aes("x", "y"), color='red', alpha=0.5, tooltips='none') + \
    geom_smooth(data=df1, mapping=aes("x", "y"), color='red') + \
    geom_point(data=df2, mapping=aes("x", "y"), color='blue', alpha=0.5, tooltips='none') + \
    geom_smooth(data=df2, mapping=aes("x", "y"), color='blue')

Expected result:
Both lines have tooltips.

From discussion.