ask knitr to hold/coalesce echos when renderings is set

fixes #12362
cc @cderv

Author: gordonwoodhull

src/resources/rmd/hooks.R

@@ -124,6 +124,11 @@ knitr_hooks <- function(format, resourceDir, handledLanguages) {
     options
   }
 
+  opts_hooks[["renderings"]] <- function(options){
+    options$fig.show = 'hold'
+    options
+  }
+
   opts_hooks[["collapse"]] <- function(options) {
     if (isTRUE(options[["collapse"]])) {
       comment <- options[["comment"]]

tests/docs/smoke-all/dark-mode/ggplot-duobrand-echo.qmd

@@ -0,0 +1,74 @@
+---
+title: "knitr dark mode - ggplot"
+brand:
+  light: united-brand.yml
+  dark: slate-brand.yml
+execute:
+  echo: false
+  warning: false
+_quarto:
+  tests:
+    html:
+      ensureHtmlElements:
+        -
+          - 'body.quarto-light'
+          - 'div.cell div.light-content'
+          - 'div.cell div.dark-content'
+          - 'div.cell div.cell-code pre.code-with-copy'
+        - []
+      ensureFileRegexMatches:
+        -
+          - 'united_theme <span class="sc">\+</span> colour_scale'
+          - 'slate_theme <span class="sc">\+</span> colour_scale'
+        - []
+---
+
+```{r}
+#| echo: false
+#| warning: false
+library(ggplot2)
+
+ggplot_theme <- function(bgcolor, fgcolor) {
+  theme_minimal(base_size = 11) %+%
+  theme(
+    panel.border = element_blank(),
+    panel.grid.major.y = element_blank(),
+    panel.grid.minor.y = element_blank(),
+    panel.grid.major.x = element_blank(),
+    panel.grid.minor.x = element_blank(),
+    text = element_text(colour = fgcolor),
+    axis.text = element_text(colour = fgcolor),
+    rect = element_rect(colour = bgcolor, fill = bgcolor),
+    plot.background = element_rect(fill = bgcolor, colour = NA),
+    axis.line = element_line(colour = fgcolor),
+    axis.ticks = element_line(colour = fgcolor)
+  )
+}
+
+brand_ggplot <- function(brand_yml) {
+  brand <- yaml::yaml.load_file(brand_yml)
+  ggplot_theme(brand$color$background, brand$color$foreground)
+}
+
+united_theme <- brand_ggplot("united-brand.yml")
+slate_theme <- brand_ggplot("slate-brand.yml")
+
+colour_scale <- scale_colour_manual(values = c("darkorange", "purple", "cyan4"))
+```
+
+### with crossref but no caption
+
+and `echo: true`
+
+::: {#fig-thematic-ggplot}
+
+```{r}
+#| echo: true
+#| renderings: [light, dark]
+ggplot(mtcars, aes(mpg, disp)) +
+  geom_point(aes(colour = factor(cyl))) + united_theme + colour_scale
+ggplot(mtcars, aes(mpg, disp)) +
+  geom_point(aes(colour = factor(cyl))) + slate_theme + colour_scale
+```
+
+:::