[api-major] Replace MissingPDFException and UnexpectedResponseException with one exception

[Snuffleupagus]

These old exceptions have a fair amount of overlap given how/where they are being used, which is likely because they were introduced at different points in time, hence we can shorten and simplify the code by replacing them with a more general ResponseException instead.

Besides an error message, the new ResponseException instances also include:

• A numeric status field containing the server response status, similar to the old UnexpectedResponseException.

• A boolean missing field, to allow easily detecting the situations where MissingPDFException was previously thrown.

[timvandermeij]

Given that this is part of the public API, and I can imagine that third-party implementations actually handle the current exceptions, should we perhaps classify this as [api-major] instead since it can be seen as a breaking change?

[Snuffleupagus]

Given that this is part of the public API, and I can imagine that third-party implementations actually handle the current exceptions, should we perhaps classify this as [api-major] instead since it can be seen as a breaking change?

I suppose that's a fair comment; I've updated the commit message and PR title.

It's been a while since we bumped the major version number, and there's also a few things in progress (e.g. canvas tiling) that are significant enough to perhaps warrant a major version bump.
Maybe we should create one last release from the 4 branch, before landing this PR?

[moz-tools-bot]

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[moz-tools-bot]

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[moz-tools-bot]

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Failed

Full output at http://54.241.84.105:8877/f562810b159cb5b/output.txt

Total script time: 28.19 mins

• Unit tests: Passed
• Integration Tests: FAILED
• Regression tests: Passed

[moz-tools-bot]

From: Bot.io (Windows)

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Failed

Full output at http://54.193.163.58:8877/328150fc0c5c6f4/output.txt

Total script time: 51.90 mins

• Unit tests: Passed
• Integration Tests: FAILED
• Regression tests: Passed

[timvandermeij]

Looks good to me, with one comment below. I do wonder if we want to wait with merging this until everything that should become part of PDF.js 5.x is identified so that in the meantime we can still make releases in the 4.x series if we need/want to?