meson subprojects command

A new --types argument has been added to all subcommands to run the command only on wraps with the specified types. For example this command will only print Hello for each git subproject: meson subprojects foreach --types git echo "Hello". Multiple types can be set as comma separated list e.g. --types git,file.

Subprojects with no wrap file are now taken into account as well. This happens for example for subprojects configured as git submodule, or downloaded manually by the user and placed into the subprojects/ directory.

The checkout subcommand now always stash any pending changes before switching branch. Note that update subcommand was already stashing changes before updating the branch.

If the command fails on any subproject the execution continues with other subprojects, but at the end an error code is now returned.

The update subcommand has been reworked:

• In the case the URL of origin is different as the url set in wrap file, the subproject will not be updated unless --reset is specified (see below).
• In the case a subproject directory exists and is not a git repository but has a [wrap-git], meson used to run git commands that would wrongly apply to the main project. It now skip the subproject unless --reset is specified (see below).
• The --rebase behaviour is now the default for consistency: it was already rebasing when current branch and revision are the same, it is less confusing to rebase when they are different too.
• Add --reset mode that checkout the new branch and hard reset that branch to remote commit. This new mode guarantees that every subproject are exactly at the wrap's revision. In addition the URL of origin is updated in case it changed in the wrap file. If the subproject directory is not a git repository but has a [wrap-git] the directory is deleted and the new repository is cloned.
• Local changes are always stashed first to avoid any data loss. In the worst case scenario the user can always check reflog and stash list to rollback.