fix(b-table): prevent endless reevaluation when using v-model and object/array literal prop values (fixes #5461)

[IwalkAlone]

Describe the PR

When using b-table with v-model, specifying certain props such as items and sortCompareOptions as object or array literals in the template would cause the browser to hang.

The cause was that computedItems depends on a chain of computed properties, some of which return a new array of items every time they're reevaluated, meaning that every reevaluation would cause the input event to be emitted. This would normally work because of computed property caching, but if a dependency was specified in the template using an object or array literal, the property would have to be recomputed each time resulting in an infinite loop. For example, the sortedItems computed property depends on items and sortCompareOptions (#5461 has an example using the latter and here is a similar example using the items prop)

The issue can be worked around by not using object and array literals in the template.

This PR adds an equality check to the computedItems watcher to prevent the looping, only emitting the input event if the array of items changed.

Fixes #5461

PR checklist

What kind of change does this PR introduce? (check at least one)

• Bugfix (fixes a boo-boo in the code) - fix(...), requires a patch version update
• Feature (adds a new feature to BootstrapVue) - feat(...), requires a minor version update
• Enhancement (augments an existing feature) - feat(...), requires a minor version update
• ARIA accessibility (fixes or improves ARIA accessibility) - fix(...), requires a patch or minor version update
• Documentation update (improves documentation or typo fixes) - chore(docs), requires a patch version update
• Other (please describe)

Does this PR introduce a breaking change? (check one)

• No
• Yes (please describe since breaking changes require a minor version update)

The PR fulfills these requirements:

• It's submitted to the dev branch, not the master branch
• When resolving a specific issue, it's referenced in the PR's title (i.e. [...] (fixes #xxx[,#xxx]), where "xxx" is the issue number)
• It should address only one issue or feature. If adding multiple features or fixing a bug and adding a new feature, break them into separate PRs if at all possible.
• The title should follow the Conventional Commits naming convention (i.e. fix(alert): not alerting during SSR render, docs(badge): update pill examples, chore(docs): fix typo in README, etc). This is very important, as the CHANGELOG is generated from these messages, and determines the next version type (patch or minor).

If new features/enhancement/fixes are added or changed:

• Includes documentation updates
• Includes component package.json meta section updates (prop, slot and event changes/updates)
• Includes any needed TypeScript declaration file updates
• New/updated tests are included and passing (required for new features and enhancements)
• Existing test suites are passing
• CodeCov for patch has met target (all changes/updates have been tested)
• The changes have not impacted the functionality of other components or directives
• ARIA Accessibility has been taken into consideration (Does it affect screen reader users or keyboard only users? Clickable items should be in the tab index, etc.)

If adding a new feature, or changing the functionality of an existing feature, the PR's
description above includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

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[codecov]

Codecov Report

Merging #5554 into dev will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               dev     #5554   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          277       277           
  Lines         9015      9016    +1     
  Branches      2496      2497    +1     
=========================================
+ Hits          9015      9016    +1     

Flag	Coverage Δ
#unittests	100.00% <100.00%> (ø)

Impacted Files	Coverage Δ
src/components/table/helpers/mixin-items.js	100.00% <100.00%> (ø)

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