feat: Calculate mediaTimeSpent based on current time

[mmustafa-tse]

Summary

• A customer noticed that the getter for mediaTimeSpent calculates the value based on the difference between mediaSessionEndTimestamp and mediaSessionStartTimestamp, which leads to inaccuracy since mediaSessionEndTimestamp is only updated when logging a media event, with this PR it now calculates based on on the difference between m.unixTimeMillis (internal function for current time) and mediaSessionStartTimestamp
• BrightScript does not support property getters like some object-oriented languages (e.g., Javascript, Kotlin and Swift), therefore a getter function on it's own was implemented on the mpCreateSGBridgeMediaApi level and to invoke it would be the same way we invoke other media functions such as logPlay(), logPause(), etc...
  m.mparticle.media.getMediaTimeSpent(mediaSession)

Testing Plan

• Was this tested locally? If not, explain why.
• E2E tested
• Assigned as a custom attribute between media events i,e: customAttributes = { "Source": "Auto Playback", "testMediaTimeSpent": m.mparticle.media.getMediaTimeSpent(mediaSession).ToStr() }
  and results are below:

Reference Issue (For mParticle employees only. Ignore if you are an outside contributor)

• Closes https://go.mparticle.com/work/SQDSDKS-7275

[BrandonStalnaker]

LGTM