Release the EGL renderer when a texture view is disposed

[YuriiKruk]

Description

HMSTextureView.disposeTextureView() now releases the EGL renderer. Before this it freed only the drawing surface, so the render thread and the EGL context stayed alive for the lifetime of the process, and every texture view that was built and then removed left one behind.

The renderer field in HMSTextureRenderer is private, so it's read reflectively.

Fixes #1858

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Additional context

Verified on a Pixel 6 by repeatedly building and disposing texture views while in a room. Debug build: 114 views created, 114 released, no renderer threads left afterwards. Release build: 81 created, 81 released, none left.

Pre-launch Checklist

• The Documentation is updated accordingly, or this PR doesn't require it.
• The ExampleAppChangelog is updated with related tickets, or this PR doesn't require it.
• I updated/added relevant documentation (doc comments with ///).
• I listed at least one issue that this PR fixes in the description above.
• I read and followed the Flutter Style Guide.
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.