include underscore after view

[mattijn]

Fix for #3024.

Now the following spec:

import altair as alt
from vega_datasets import data
iris = data.iris.url

alt.Chart(iris).mark_point().encode(
    alt.X(alt.repeat("column"), type='quantitative'),
    alt.Y(alt.repeat("row"), type='quantitative'),
    color='species:N'
).properties(
    width=200,
    height=200
).repeat(
    row=['petalLength', 'petalWidth'],
    column=['sepalLength', 'sepalWidth']
).interactive().to_dict()

Returns

{'config': {'view': {'continuousWidth': 300, 'continuousHeight': 300}},
 'repeat': {'column': ['sepalLength', 'sepalWidth'],
  'row': ['petalLength', 'petalWidth']},
 'spec': {'data': {'url': 'https://cdn.jsdelivr.net/npm/vega-datasets@v1.29.0/data/iris.json'},
  'mark': {'type': 'point'},
  'encoding': {'color': {'field': 'species', 'type': 'nominal'},
   'x': {'field': {'repeat': 'column'}, 'type': 'quantitative'},
   'y': {'field': {'repeat': 'row'}, 'type': 'quantitative'}},
  'height': 200,
  'name': 'view_1',
  'width': 200},
 'params': [{'name': 'param_1',
   'select': {'type': 'interval', 'encodings': ['x', 'y']},
   'bind': 'scales',
   'views': ['view_1_child__row_petalLengthcolumn_sepalLength',
    'view_1_child__row_petalLengthcolumn_sepalWidth',
    'view_1_child__row_petalWidthcolumn_sepalLength',
    'view_1_child__row_petalWidthcolumn_sepalWidth']}],
 '$schema': 'https://vega.github.io/schema/vega-lite/v5.7.1.json'}

Focus on:

'view_1_child__row_petalWidthcolumn_sepalLength'

[mattijn]

Tests pass, merging.