feat: shim injectIntl rather than expecting it from frontend-base

[bradenmacdonald]

To go along with openedx/frontend-base#288 , this PR shims injectIntl and intlShape for full backwards compatibility.

Note: the implementation is different than frontend-platform's injectIntlWithShim since the goal here is just basic functionality, not preserving the custom logging functionality.

Claude helped me write this and did some tests but I haven't properly tested it in an MFE.

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