textplot_xray() from kwic() based on dictionary pattern

[kbenoit]

I thought that in #1515, we fixed kwics to plot (in textplot_xray()) by dictionary key, not value. But it appears to be faceting on values, not keys.

library("quanteda")
## Package version: 1.4.4

# one facet per value
dict <- dictionary(list(
  preps = c("to", "of", "for"),
  articles = c("the", "an", "an")
))
corp <- corpus_subset(data_corpus_inaugural, Year %in% c(1945, 1865))
kwicdict <- kwic(corp, pattern = dict)
textplot_xray(kwicdict)

# one facet per key
tokens(corp) %>%
  tokens_lookup(dictionary = dict, exclusive = FALSE, capkeys = TRUE) %>%
  kwic(pattern = char_toupper(names(dict))) %>%
  textplot_xray()

Is that what we intended? The second form is not likely to be easy for users to apply.