Fix #7387: Specify buffers in regl.clear() to avoid performance warning

[MzyzzG]

This PR fixes issue #7387 by specifying the color and depth buffers in the regl.clear() call in src/traces/scattergl/plot.js. This prevents the "Performance warning: clear() called with no buffers in bitmask" warning.

Changes:

• Modified regl.clear({}) to regl.clear({ color: true, depth: true }).

[archmoj]

This PR looks good to me.
💯 🙏 Many thanks @zachchan-voltaiq
Thanks to @emilykl's #7396 and in order for the failing tests to pass you could fetch upstream/master and merge it into your PR branch.

Please add a draft log as described here: https://github.com/plotly/plotly.js/tree/master/draftlogs

Also it would be great if you add a jasmine test possibly in test/jasmine/tests/scattergl_test.js to lock the bug you fixed in this PR.

Thank you!