CustomSelectControlV2: fix select popover content overflow

[ciampo]

What?

Part of #55023

Set a minimum width for the CustomSelectControl V2's select popover

Why?

To avoid content overflowing or horizontal scrolling inside the popover

How?

• add min-width: fit-content to the popover wrapper to avoid the content from overflowing
• set the prop slide={false} on Ariakit's SelectPopover to keep the popover anchored to its trigger while scrolling the page horizontally

Testing Instructions

1. Apply these changes:

Click to expand

diff --git a/packages/components/src/custom-select-control/stories/index.story.tsx b/packages/components/src/custom-select-control/stories/index.story.tsx
index 8ff9a023c5..e9f21cfa0f 100644
--- a/packages/components/src/custom-select-control/stories/index.story.tsx
+++ b/packages/components/src/custom-select-control/stories/index.story.tsx
@@ -90,7 +90,7 @@ WithLongLabels.args = {
 		},
 		{
 			key: 'reallylonglabel2',
-			name: 'But they can take a long time to type.',
+			name: 'Buttheycantakealongtimetotype.',
 		},
 		{
 			key: 'reallylonglabel3',

2. Load the CustomSelectControlV2 Legacy "With Long Labels" story
3. Open the select dropdown and resize the page horizontally — make sure that the popover stops resizing once it reaches its minimum allowed width, and that the popover content never overflows / causes horizontal scroll inside the popover
4. Load the same "With Long Labels" story, but for the V1 version of the component, and make sure that the behaviour is the same.

Screenshots or screencast

Version	screencast
V1	cscv1.-.item.wrapping.mp4
V2, before (trunk)	cscv2.-.item.wrapping.-.before.mp4
V2, after (this PR)	cscv2.-.item.wrapping.-.after.mp4

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Co-authored-by: ciampo <mciampini@git.wordpress.org>
Co-authored-by: mirka <0mirka00@git.wordpress.org>

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[mirka]

Good one 👍