feat: support `Index.to_frame()`

[mattyopl]

Intern Starter Task

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can test by checking:

import pandas as pd
idx = pd.Index(['Ant', 'Bear', 'Cow'], name='animal')
df = idx.to_frame()
print(df)
df = idx.to_frame(False)
print(df)
df = idx.to_frame(name = "food")
print(df)
df = idx.to_frame(False, name = "food")
print(df)

import bigframes.core as core
idx = core.indexes.Index(['Ant', 'Bear', 'Cow'], name='animal')
df = idx.to_frame()
print(df)
df = idx.to_frame(False)
print(df)
df = idx.to_frame(name = "food")
print(df)
df = idx.to_frame(False, name = "food")
print(df)

Fixes internal 356891401 🦕