fix: Use correct offset in snapshot

[mofojed]

• Was using row.offsetInSnapshot, which was a "protected" API and recently removed from the JS API
• API was removed in JS API refactoring: refactor: Rewrite JS API to share server implementation of Flight/Barrage deephaven-core#5890
• Instead just use the viewport offset and add the index of the row in the snapshot, which is there in both versions of the API
  • New API does support row.index, but this way is compatible with both
• Updated unit tests
• Tested using a deephaven.ui.list_view:

from deephaven import time_table, ui
import datetime

initial_row_count = 200
column_types = time_table(
    "PT1S",
    start_time=datetime.datetime.now() - datetime.timedelta(seconds=initial_row_count),
).update(
    [
        "Id=new Integer(i)",
        "Display=new String(`Display `+i)",
    ]
)

@ui.component
def ui_list_view_table():
    value, set_value = ui.use_state([])

    lv = ui.list_view(
        column_types,
        aria_label="List View",
        on_change=set_value,
        selected_keys=value,
    )

    text = ui.text("Selection: " + ", ".join(map(str, value)))

    return ui.flex(
        lv,
        text,
        direction="column",
        margin=10,
        gap=10,
        width=500,
        # necessary to avoid overflowing container height
        min_height=0,
    )

lv_table = ui_list_view_table()

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 46.77%. Comparing base (99b8d59) to head (d789b90).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    deephaven/web-client-ui#2217      +/-   ##
==========================================
- Coverage   46.78%   46.77%   -0.01%     
==========================================
  Files         694      694              
  Lines       38627    38625       -2     
  Branches     9659     9780     +121     
==========================================
- Hits        18070    18068       -2     
+ Misses      20546    20504      -42     
- Partials       11       53      +42     

Flag	Coverage Δ
unit	46.77% <100.00%> (-0.01%)	⬇️

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[mofojed]

e2e tests are failing due to deephaven/deephaven-core#6056
Forcing this one to merge as it fixes an issue that is affecting the e2e tests for deephaven-plugins.