[5.7][android] Update to LTS NDK 25b (#60938)

[finagolfin]

Cherrypick of 5.7-relevant portions of #60938 and single doc change from #61873

Explanation: Make it so that the Swift build detects the clang shipping in the Android NDK, rather than having to manually update SWIFT_ANDROID_NDK_CLANG_VERSION every time, by extracting the versioned resource directory from the NDK using file(GLOB).

Scope: Only affects cross-compiling for Android with the NDK

SR Issue: None

Risk: Essentially none, since it only affects Android

Testing: This patch got trunk compiling on the community Android CI again with the latest NDK 25b.

Reviewer: @DougGregor

This pull will keep 5.7 patch releases compiling with future NDK releases, rather than having to manually patch this repo with the new clang version each time. Since this pull is so low-risk, I thought it is worth getting in to 5.7.

[finagolfin]

Ping @DougGregor, please let me know if we can get this small pull in.

[finagolfin]

Ping, now that 5.7.1 is out, would be good to get this in before 5.7.2.

[finagolfin]

@shahmishal, could we get this small pull in?

[airspeedswift]

Always put a link to the original change in description of all PRs that pick to 5.7 (unless there's some exceptional reason why that doesn't apply, in which case explain why in the PR description)

[finagolfin]

Always put a link to the original change in description of all PRs that pick to 5.7

@airspeedswift, done, guess I forgot this time.

[finagolfin]

Ping, would like to get this in.

[finagolfin]

Pinging @airspeedswift, can we get this small pull in for Android?

[finagolfin]

@DougGregor, can we get this small Android pull in before the next patch release?

[finagolfin]

@shahmishal, would like to get this small change in before the next patch release, or at least a decision made. It's a small tweak that only affects building the stdlib for Android, so I figured it's safe to get in.

[finagolfin]

Closing since 5.8 was just released, which already has this pull.