Provide a CLI option to run cargo commands from the root of a workspace

[sunshowers]

Describe the problem you are trying to solve
I'd like to define a Cargo alias which encodes a file path that's relative to the root of the workspace. Currently, there appears to be no way to define a Cargo alias that works from any subdirectory, because:

• aliases run from the cwd, not the root (which makes sense)
• you can't run, e.g. cd (or multiple commands in general) in a Cargo alias

Describe the solution you'd like

A new global flag to cargo, e.g. --root-cwd, which runs the command and interprets paths relative to the root of the workspace. (It can be defined to be equivalent to cd $WORKSPACE_ROOT && cargo <command>....)

This may also be paired with a --cwd option which runs the command and interprets paths relative to the given cwd. (Again, cargo --cwd CWD <command>... can be defined to be equivalent to cd $CWD && cargo <command>....)

Notes

Some prior art: Mercurial has the --cwd flag which has this behavior: https://www.mercurial-scm.org/doc/hg.1.html#options. Not sure about Git.