feat: handle saving multiple files

[jguegel]

Type of change(s)

• Bug fix
• Feature / enhancement
• Infrastructure / tooling (CI, build, deps, tests)
• Documentation

What changed and why

• Added intent for multiple file "save as"-share menu
• Added @Suppress("TooManyFunctions") to avoid detekt error with too many functions in SaveAsActivity
• No UI change
• Using same behavior like sanitizeFilename & findAvailableName
• Added new strings (files_saved, files_saved_partially)

Closes the following issue(s)

• Closes "Save as" in the share menu not available when multiple files are selected #345

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator (if applicable).
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• All checks are passing.

[naveensingh]

This is just a quick review.

FYI: Conventional commits (and PR title) are preferred. This is mentioned in https://github.com/FossifyOrg/General-Discussion#contributing-code (point 3). "added:" is not a valid type.

[jguegel]

thanks for the feedback, didn't know about the plural strings
fyi i will be out till february