[Autocomplete] fix unintended focus in autocomplete

[atharva3333]

Fixes - #47661

This issue occurs when the popup of one Autocomplete overlaps another Autocomplete.

Reproduction Steps

1. Focus an Autocomplete to open its popup.
2. Click outside the browser window (without minimizing it).
3. Click and hold the mouse button on the border of another overlapping Autocomplete.

Observed Behavior

During the mousedown phase (before mouseup):

• The previously focused Autocomplete regains focus.
• For a normal Autocomplete, this causes an unintended label shrink.
• For openOnFocus, the popup opens (since its getting focused) during the mouse hold and select an option on mouse release.

This behavior appears to be triggered by the following logic inside handleMouseDown:

if (event.target.getAttribute('id') !== id) {
  event.preventDefault();
}

• I have followed (at least) the PR section of the contributing guide.

[mui-bot]

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Bundle size report

Bundle	Parsed size	Gzip size
@mui/material	🔺+202B(+0.04%)	🔺+31B(+0.02%)
@mui/lab	0B(0.00%)	0B(0.00%)
@mui/system	0B(0.00%)	0B(0.00%)
@mui/utils	0B(0.00%)	0B(0.00%)

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