Extract all interval labels from a tier in a single operation, instead of calling `textgrid$get_interval_text()` repeatedly.
Examples
tg <- TextGrid$create(0, 1, "words")
tg$insert_boundary(1, 0.5)
tg$set_interval_text(1, 2, "hello")
labels <- get_textgrid_labels_all(tg, tier = 1)
table(labels) # Frequency table of labels
#> labels
#> hello
#> 1 1