`model_parameters`: Add variables names for `chisq.test` objects

Working on easystats/report#309 and experiencing the continuous joy of htest objects.

For example, model_parameters on a cor.test object will provide the names of the variables:

x <- cor.test(mtcars$mpg, mtcars$drat)
parameters::model_parameters(x)
#> Pearson's product-moment correlation
#> 
#> Parameter1 |  Parameter2 |    r |       95% CI | t(30) |      p
#> ---------------------------------------------------------------
#> mtcars$mpg | mtcars$drat | 0.68 | [0.44, 0.83] |  5.10 | < .001
#> 
#> Alternative hypothesis: true correlation is not equal to 0

Which report then relies on to report the test. But model_parameters does not report the variable names for chisq.test objects:

m <- as.table(rbind(c(762, 327, 468), c(484, 239, 477)))
dimnames(m) <- list(gender = c("F", "M"), party = c("Democrat", "Independent", "Republican"))
x <- chisq.test(m)

parameters::model_parameters(x)
#> Pearson's Chi-squared test
#> 
#> Chi2(2) |      p
#> ----------------
#> 30.07   | < .001

Yet the variable names seem available:

attributes(x$observed)
#> $dim
#> [1] 2 3
#> 
#> $dimnames
#> $dimnames$gender
#> [1] "F" "M"
#> 
#> $dimnames$party
#> [1] "Democrat"    "Independent" "Republican" 
#> 
#> 
#> $class
#> [1] "table"

Fixing this would allow me to fix the current bug with chisq.test objects in report.

report::report(x)
#> Error in UseMethod("interpret"): no applicable method for 'interpret' applied to an object of class "NULL"

^{Created on 2023-08-27 with reprex v2.0.2}

Start at model_parameters handling for chisq.test objects and reproduce the issue using the R examples in the report. Inspect how the observed table's dimnames are available, then verify that model_parameters exposes the variable names and that report::report(x) no longer fails with missing parameter information.