Consider functions instead of alias

[hohwille]

In IDEasy we currently define ide as an alias to sourcing a script.
For auto-completion we also hook in via a sourced bash script (source $IDE_ROOT/_ide/completion).
With #778 a new such command is to be added that also needs autocompletion.

An alternative could be to use bash functions instead:

• Instead of having an ide script in $IDE_ROOT/_ide/bin we can have $IDE_ROOT/functions.
• Instead of adding aliases, sourcing multiple scripts, etc. we would just add a source $IDE_ROOT/functions to .bashrc / .zshrc.
• In functions we can also check if we are in zsh and install autocompletion to simplify setup and uninstallation of IDEasy if all we need might be a single line of code in .bashrc / .zshrc.
• This functions "script" that is sourced can define bash functions such as ide and icd instead that we use alias for that.

IMHO this will simplify and increase flexibility for future extension (e.g. if we have more ideas like #778), since we only need to tweak .bashrc once and forever and newer releases of IDEasy can add new commands and completions all via functions.
The first step with this story should be an analysis and PoC testing if this plan works well or there are some drawbacks of this idea.
If all works as planned, we should implement it this way since it seems the superior design.

[hohwille]

For the record: I decided for High as priority since this is a refactoring that will impact existing installations on roll-out / upgrade.
If this approach works out, it is better to have it soon before many projects and users will start installing and using IDEasy.