[v2] Upgrade prompt-toolkit to 3.0.51

[hssyoo]

Fixes #9453

Upgrades prompt-toolkit ceiling to 3.0.51.

prompt-toolkit began identifying its package version using importlib.metadata [source]. This is increasingly becoming a common pattern so I made a couple long-term decisions to unblock the upgrade.

• The AWS CLI wraps default import finders in a custom class [source]. This decision was made early in v2 when botocore and s3transfer were vended so that existing code wouldn't need to update its imports. This prevents prompt-toolkit's metadata from being found at build time and runtime. I fixed this by instead inserting the custom wrapped import finder before the default import finder. So imports will continue working as it always has, but if it fails to load metadata, it'll fall back to the default import finder. I think in the long term we should just remove the custom import finder code altogether and make the effort to update imports (eg import botocore -> import awscli.botocore.
• Package metadata is found in their respective dist.info directories. Our build code was intentionally removing these files from the final distribution because they were unnecessary at the time. I removed that logic since we now need package metadata at runtime.

[hssyoo]

Okay so prompt-toolkit began identifying its version using importlib.metadata.version [source]. There are 2 issues here..

1. The AWS CLI looks for certain path finders and wraps them inside a custom path finder [source]. This prevents prompt-toolkit's metadata from being found at build time and runtime.
2. PyInstaller doesn't copy package metadata by default when building the frozen executable. This prevents prompt-toolkit's metadata from being found at runtime. There's a way to configure this, but I haven't gotten it to work yet [docs].