feat(ruby): improve bump/widen strategy for ~>

[qnighy]

Changes

This PR changes how Renovate updates Ruby's Gemfile to be more consistent. It includes the following changes:

• Changes to ~> range
  • In bump and replace strategies, the precision in ~> will never be changed as the implicit upper bound relies on the precision.
    • Instead, in bump strategy, it adds or removes the corresponding >= range to represent the exact lower bound.
  • In widen strategy, it decomposes ~> to >= and < ranges.
• Changes to != range
  • In bump strategy, it tries to convert != into >= range.
• Changes to <, <= ranges
  • The behaviors for < and <= are now consistent with each other.
  • In bump, replace, and widen strategies, it updates these ranges only if the new version violates them.
• Changes to >, >= ranges
  • The behaviors for > and >= are now consistent with each other.
  • In bump strategy, it always updates the range so that the lower bound sticks with the new version.
  • In replace and widen strategies, it updates these ranges only if the new version violates them. (This is supposed to be a rare case)

Context

This PR is a second attempt at #11130.

The most important motivation is that Renovate sometimes updates ~> in a way that the upper bound is unintentionally tightened.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please tick one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[renovate-release]

🎉 This PR is included in version 32.160.0 🎉

The release is available on:

• GitHub release
• 32.160.0

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