patch 9.1.1732: filetype: .inc file detection can be improved

patch 9.1.1732: filetype: .inc file detection can be improved

Problem:  filetype: .inc file detection can be improved
Solution: Update filetype detection for Pascal and BitBake code
          (Martin Schwan).

Fix the detection of .inc files containing Pascal and BitBake code:

- the concatenated string, merged from three lines, only contains one
  beginning and the pattern "^" would not match as expected. Use a range()
  loop to iterate each line string individually. This way, the pattern "^"
  works for beginning of lines.

- improve BitBake include file detection by also matching forward-slashes
  "/" in variable names and assignment operators with a dot ".=" and "=.".
  Valid examples, which should match, are:

    PREFERRED_PROVIDER_virtual/kernel = "linux-yocto"
    MACHINEOVERRIDES =. "qemuall:"
    BBPATH .= ":${LAYERDIR}"

- parse twenty instead of just three lines, to accommodate for potential
  comments at the beginning of files

closes: #18202

Signed-off-by: Martin Schwan <m.schwan@phytec.de>
Signed-off-by: Christian Brabandt <cb@256bit.org>