ci: show the size of the build next to main in the job summary

The bank growth step only exported the sizes to the environment since the
comment that used them was removed, so nothing showed them any more. It now
writes a table of the code banks, XSEG, the stack left after the internal
RAM is allocated and the web assets, main against the branch, to the job
summary, which needs no write permission on the pull request.

tools/size_summary.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+seg() {
+	sed -rn "s/^$1[^=]*=\\s+([0-9]+)\\. bytes.*$/\\1/p" "$2/rtlplayground.map" | head -n 1
+}
+stack() {
+	sed -rn 's/.* with ([0-9]+) bytes available.*/\1/p' "$1/rtlplayground.mem"
+}
+row() {
+	echo "| $1 | $2 | $3 | $((${3:-0} - ${2:-0})) |"
+}
+echo "### KP_9000_6XHML_X2"
+echo
+echo "| | main | branch | change |"
+echo "| --- | ---: | ---: | ---: |"
+for s in HOME CSEG BANK1 BANK2 BANK3 BANK4 XSEG; do
+	row "$s" "$(seg $s "$1")" "$(seg $s "$2")"
+done
+row "stack available" "$(stack "$1")" "$(stack "$2")"
+row "web" "$(du -sb "$3" | cut -f1)" "$(du -sb "$4" | cut -f1)"