qmake2cmake: convert qmake INSTALLS targets to cmake install commands

implement "postinstall" commands

example input

target.path = /dst
target.extra = echo hello world

another_target.path = /dst
another_target.files = a.txt
another_target.depends = target

INSTALLS = target another_target

cmake has no equivalent construct, so my implementation works by adding a series of install commands, which cmake will execute in order of appearance. qmake2cmake resolves the install order from the target dependencies

# install_target
install(CODE [[
  message(STATUS "Installing: /tmp/a.txt")
  execute_process(
    COMMAND echo hello world
    COMMAND_ERROR_IS_FATAL ANY
  )
]])

# install_another_target
# depends on: install_target
install(CODE [[
  message(STATUS "Installing: /tmp/a.txt")
  file(COPY /src/a.txt DESTINATION /dst/a.txt)
]])

please see my patches in
https://github.com/milahu/qmake2cmake/tree/fix-for-pyqt-builder
i have little motivation to mess with qt's gerrit interface, so please feel free to use my code

status: working prototype

this works to build pyqt6
pyqt-builder generates qmake .pro files
and instead of qmake, i call qmake2cmake_all and cmake

with pyqt-builder, im hitting a non-trivial bug in qmake_parser.py:
the original whitespace is lost in scope.get_string(key)
but there is a simple workaround: use quoted strings in the .pro file
i will post this in a separate issue