[Doc] Update KernelProgramCache.md with details on in-memory eviction

[uditagarwal97]

This PR updates KernelProgramCache.md by:

1. Making the doc in-sync with recent changes in in-memory cache (Like [SYCL] Remove CompileOpts and LinkOpts from Cachekey #11351)
2. Adding details of in-memory cache eviction ([SYCL] Implement eviction for in-memory program cache #16062)

Partially fixes: #16017

[maarquitos14]

UR is added in this new changes, but there are still plenty of mentions to PI throughout the document. Can we get them updated? PI does no longer exist.

Also, I like this kind of documents to be self-contained, so I don't like us pointing readers to EnvironmentVariables.md in Cache Configuration section. That's just a matter of style, so I will not block approval based on this, but I would like to have the environment variables listed in this document to make it easier for readers.

[maarquitos14]

@steffenlarsen since you reviewed #16062 too, you might want to take a look at this as well.

[steffenlarsen]

A couple of comments, mostly editorial and for consistency.

[uditagarwal97]

UR is added in this new changes, but there are still plenty of mentions to PI throughout the document. Can we get them updated? PI does no longer exist.

Also, I like this kind of documents to be self-contained, so I don't like us pointing readers to EnvironmentVariables.md in Cache Configuration section. That's just a matter of style, so I will not block approval based on this, but I would like to have the environment variables listed in this document to make it easier for readers.

In e24d975, I've removed remaining PI references and added cache-related environment variables in this doc itself.

[steffenlarsen]

LGTM!

[maarquitos14]

Just a nit, otherwise LGTM.

[uditagarwal97]

@intel/llvm-gatekeepers the PR is ready to be merged.