Python launcher does not filter when only one runtime is installed

[zooba]

If the launcher only finds a single runtime, it skips all filtering, which means if you request a mismatched version you will still get the installed one.

e.g. a user (let's call them "Guido") installs Python 3.11. They then run py -3.12 and instead of suggesting to install 3.12, it launches 3.11!

Unrelated, but discovered at the same time: -3.1 will match -3.11, because it's a blind prefix match. The match should require a separator character.

Linked PRs

• gh-101467: Correct py.exe handling of prefix matches and cases when only one runtime is installed #101468
• [3.11] gh-101467: Correct py.exe handling of prefix matches and cases when only one runtime is installed (GH-101468) #101504