Add support for strict JSON comparison in WebTestClient

[elgleidson]

Support for expectedBody().json(<expected strict json>, true);

Part of the code base already has support - via JsonExpectationsHelper - but WebTestClient has no method to use the strict version. The existing method uses lenient, which is not always desired.

Example:
Let's say /persons/1/ returns the following response:

{
  "name":"John",
  "surname":"Smith"
}

The following test works fine:

webTestClient.get()
    .uri("/persons/1")
    .accept(MediaType.APPLICATION_JSON)
    .exchange()
    .expectStatus().isOk()
    .expectBody().json("{\"name\":\"John\"}");

I'm just adding a new method so that we can use strict comparison when appropriate.

Example:

This test fails because the response has more fields than expected and we're using strict mode:

webTestClient.get()
    .uri("/persons/1")
    .accept(MediaType.APPLICATION_JSON)
    .exchange()
    .expectStatus().isOk()
    .expectBody().json("{\"name\":\"John\"}", true);

But the following test passes because we're expecting all fields:

webTestClient.get()
    .uri("/persons/1")
    .accept(MediaType.APPLICATION_JSON)
    .exchange()
    .expectStatus().isOk()
    .expectBody().json("{\"name\":\"John\",\"surname\":\"Smith\"}", true);

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[sbrannen]

It looks like the code examples for The following test works fine and This test fails are identical. Can you please update this PR's description?

[elgleidson]

It looks like the code examples for The following test works fine and This test fails are identical. Can you please update this PR's description?

Done.

[sbrannen]

This has been merged into 5.3.x and main in 920be8e and slightly revised in eb84c84.

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