Add onKeyringRequest to snaps-jest

[david0xd]

Add possibility to test onKeyringRequest with snaps-jest.

Fixes: #2775

Keyring test example:

describe("onKeyringRequest", () => {
  it("sends keyring request", async () => {
    const { onKeyringRequest } = await installSnap();

    const response = await onKeyringRequest(
      {
        origin: "https://metamask.github.io",
        params: {
          options: {
            privateKey: "foo bar"
          }
        },
        method: "keyring_createAccount"
      });

    expect(response).toBe({ /* Add expected result here */ });
  });
});

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.44%. Comparing base (fae7855) to head (8301727).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2777   +/-   ##
=======================================
  Coverage   94.44%   94.44%           
=======================================
  Files         484      484           
  Lines       10309    10314    +5     
  Branches     1567     1567           
=======================================
+ Hits         9736     9741    +5     
  Misses        573      573           

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