fix(types): allow readonly arrays for data matcher in types

[laurence-myers]

fixes #2174

Changes the definition of DataMatcherArray, from this:

interface DataMatcherArray extends Array<DataMatcher> {}

To this:

interface DataMatcherArray extends ReadonlyArray<DataMatcher> {}

Refer to #2174 for details.

I also added .idea to .gitignore, to ignore project files generated by IntelliJ IDEA. (I assume that's okay, since .gitignore already lists .vscode.)

[laurence-myers]

I wasn't sure which branch to target. The contributing guide says generally to merge to beta, but that branch doesn't seem to exist (anymore).

[gr2m]

The contributing guide says generally to merge to beta

We should update the contributing guide, we wrote it at a time of big refactoring when beta was the branch we collaborated on, but that's done now

[gr2m]

@all-contributors add @laurence-myers for code

[allcontributors]

@gr2m

I've put up a pull request to add @laurence-myers! 🎉

[github-actions]

🎉 This PR is included in version 13.1.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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