Rework CI workflows (#8688)

- split workflows into separate files to trigger by path
  this should help out documentation and boards / eboot / pkg files
  updates, since those *wont* trigger usual build stuff anymore
- build*.sh whatever merged into just common.sh and build.sh
  trigger different parity builds, mod % rem and allow to set .ino list
  through the environment variable
- removes unnecessary temporary files, try to use more pipes
  move remaining ones into cache dir instead of PWD
- remove legacy TRAVIS env vars, use ESP8266_ARDUINO prefix for config
- remove Windows path workarounds
- hardware/ and ide/ directories are set through envionment
  do not force specific paths, simplify builds on local machine
- sketch list is set through environment. expicit paths for Windows and
  macOS builders. platformio also gets a real shuffled list instead of
  mod and rem magic numbers
- detect root of the repo through git cli, not base{name,dir} or relative paths

tests/ci/eboot_test.sh

@@ -1,13 +1,14 @@
 #!/bin/bash
 
-READELF="$TRAVIS_BUILD_DIR/tools/xtensa-lx106-elf/bin/xtensa-lx106-elf-readelf"
-
 set -ev
 
-cd $TRAVIS_BUILD_DIR/tools
+root=$(git rev-parse --show-toplevel)
+READELF="$root/tools/xtensa-lx106-elf/bin/xtensa-lx106-elf-readelf"
+
+cd $root/tools
 python3 get.py -q
 
-cd $TRAVIS_BUILD_DIR/bootloaders/eboot
+cd $root/bootloaders/eboot
 
 "$READELF" -x .data -x .text eboot.elf > git.txt
 make clean