WebGL: Add offline support

[melekr]

Context

WebGL users can lose unsent Backtrace reports when:

• BacktraceDatabase writes aren’t flushed from IDBFS to IndexedDB before tab close/background.

and/or

• BacktraceDatabase is disabled/unavailable, causing network/server send failures to be dropped.

Solution

Persist offline reports reliably (IDBFS flush hooks + PlayerPrefs fallback queue)

This PR adds two WebGL-specific reliability layers consistent with existing Backtrace database settings:

1. IDBFS flush support

• Adds BacktraceSync.jslib exposing FS.syncfs
• Adds BacktraceWebGLSync.cs wrapper
• Installs page lifecycle hooks (pagehide, beforeunload, visibilitychange, freeze) and calls FS.syncfs at key SDK lifecycle points to reduce data loss.

2. Fallback offline queue when BacktraceDatabase is unavailable:

• Adds WebGLOfflineDatabase.cs PlayerPrefs queue.
• Queue bounds derive from BacktraceConfiguration database settings (MaxRecordCount, MaxDatabaseSize, RetryLimit, RetryOrder, RetryInterval, AutoSendMode)
• Enforces WebGL safe hard caps to avoid excessive PlayerPrefs/browser storage use
• Replays queued reports on an interval when AutoSendMode is enabled.

Notes / Limitations

• FS.syncfs is best-effort and async: abrupt tab termination can still lose data.
• PlayerPrefs queue is intentionally bounded: oversized reports are not persisted.

Sample Reports

ref: BT-6231

[konraddysput]

BacktraceClient represents a business logic not related to the database. We have a dedicated class implementation for it, which is BacktraceDatabase. Mixing business logic and database implementation in the client is the wrong decision long term. Instead, you need to use BacktraceDatabase and use abstraction to properly implement a proper database logic for webgl /webgl database operations.

Please also look at the project structure to follow the file pattern.

[konraddysput]

we already have a static Backtrace instance available here.

[konraddysput]

It should be moved to BacktraceDatabase - BacktraceDatabase offerts the same Untiy scope.

[konraddysput]

It should be abstracted in the BacktraceDatabase implementation - we have the Start/Awake support there.

[melekr]

BacktraceClient represents a business logic not related to the database. We have a dedicated class implementation for it, which is BacktraceDatabase. Mixing business logic and database implementation in the client is the wrong decision long term. Instead, you need to use BacktraceDatabase and use abstraction to properly implement a proper database logic for webgl /webgl database operations.

Please also look at the project structure to follow the file pattern.

webgl db logic can be easily moved out of BacktraceClient, and the implementation above does not affect platforms other than the currently unsupported webgl. ~

The fine-line/strategy -here- was to diverge temporarily and quickly unblock webgl integrators while we work on providing real targeted support for webgl as a first-class platform (rather than relying on default/general/other platforms implementations).

If this PR adds too much noise, we can close it and work on webgl offline support after/under the broader webgl scope.