1.0.0: update ggtranscript to work with the latest versions of R, ggplot2 and ggrepel

[dzhang32]

Summary of changes

• Fixes https://github.com/dzhang32/ggtranscript/issues/13 and https://github.com/dzhang32/ggtranscript/issues/10
  • Newer version of ggplot2 deprecated "size" in favour of "linewidth"
  • Replaces "size" with "linewidth"
• Fixes https://github.com/dzhang32/ggtranscript/issues/8
  • "y_orig" conflicted with a variable name in the newer version ggrepel.
  • Replaces "y_orig" with "y_original".
• Fixes all unit tests, updating snapshots where needed.
• Updates CI workflow to use the latests R/bioconductor versions and simplifies it to testing on linux-only.
• Fixes any R CMD Check issues.