This is the mirror image of #2170.

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- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
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Add `default_converter` argument to `to_js` and `toJs`. This is the mirror image of #2170.

### Checklists

<!-- Note on checklists:
     If you think some of these steps are not necessary for your PR,
     just remove those checkboxes, or mark them as checked. Otherwise,
     if some checkboxes are left unmarked, we might assume that your PR
     is not ready to be merged and we might keep you waiting -->

- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
- [x] Add / update tests
- [x] Add new / update outdated documentation

# from: parakeet testbed
# setup: import numpy as np ; M, N = 512, 512 ; X = np.random.randn(M,N)
# run: harris(X)

# pythran export harris(float64[][])


def harris(X):
    m, n = X.shape
    dx = (X[1:, :] - X[: m - 1, :])[:, 1:]
    dy = (X[:, 1:] - X[:, : n - 1])[1:, :]

    #
    #   At each point we build a matrix
    #   of derivative products
    #   M =
    #   | A = dx^2     C = dx * dy |
    #   | C = dy * dx  B = dy * dy |
    #
    #   and the score at that point is:
    #      det(M) - k*trace(M)^2
    #
    A = dx * dx
    B = dy * dy
    C = dx * dy
    tr = A + B
    det = A * B - C * C
    k = 0.05
    return det - k * tr * tr

# from: parakeet testbed
# setup: import numpy as np ; M, N = 512, 512 ; X = np.random.randn(M,N)
# run: harris(X)

# pythran export harris(float64[][])


def harris(X):
    m, n = X.shape
    dx = (X[1:, :] - X[: m - 1, :])[:, 1:]
    dy = (X[:, 1:] - X[:, : n - 1])[1:, :]

    #
    #   At each point we build a matrix
    #   of derivative products
    #   M =
    #   | A = dx^2     C = dx * dy |
    #   | C = dy * dx  B = dy * dy |
    #
    #   and the score at that point is:
    #      det(M) - k*trace(M)^2
    #
    A = dx * dx
    B = dy * dy
    C = dx * dy
    tr = A + B
    det = A * B - C * C
    k = 0.05
    return det - k * tr * tr
