Refactor IO-related code to use the new LoadOptions interface

[caisq]

• Refactor several IO-related functions to use the new LoadOptions interface.
• Move monitorProgress to the io-specific source directory.

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This change is 

[nsthorat]

Ideally we get this in this week before 1.0, is that right?

[nsthorat]

(let me know when to review)

[caisq]

@nsthorat There are a bunch of conflicts to resolve. I'll let you know when it's ready.

[caisq]

@nsthorat @dsmilkov @pyu10055 ready for review.

[nsthorat]

Reviewed 4 of 7 files at r1, 3 of 3 files at r2.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @caisq, @dsmilkov, @nsthorat, and @pyu10055)

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src/io/progress.ts, line 39 at r2 (raw file):

  let resolvedPromise = 0;

  function registerMonitor(promise: Promise<{}>) {

for these private functions can you create them like this so it's clear they're not top-level:

const registerMonitor = promise => ...

[dsmilkov]

Reviewed 1 of 7 files at r1, 1 of 3 files at r2.
Reviewable status: complete! 2 of 1 approvals obtained (waiting on @caisq, @dsmilkov, and @pyu10055)

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src/io/browser_http.ts, line 448 at r2 (raw file):

 * 'model.weights.bin') will be appended to the body. If `requestInit` has a
 * `body`, an Error will be thrown.
 * @param weightPathPrefix Optional, this specifies the path prefix for weight

update jsdocs

[caisq]

Reviewable status: complete! 2 of 1 approvals obtained (waiting on @pyu10055)

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src/io/browser_http.ts, line 448 at r2 (raw file):

Previously, dsmilkov (Daniel Smilkov) wrote…

update jsdocs

Done.

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src/io/progress.ts, line 39 at r2 (raw file):

Previously, nsthorat (Nikhil Thorat) wrote…

for these private functions can you create them like this so it's clear they're not top-level:

const registerMonitor = promise => ...

Done.