Backported PRs:
- [x] #55480 <!-- Fix push! for OffsetVectors, add tests for push! and
append! on AbstractVector -->
- [x] #55443 <!-- Add test for upper/lower/titlecase and fix call -->
- [x] #55524 <!-- Set `.jl` sources as read-only during installation -->
- [x] #55500 <!-- make jl_thread_suspend_and_get_state safe -->
- [x] #55506 <!-- Fix indexing in _mapreducedim for OffsetArrays -->
- [x] #55564 <!-- Empty out loaded_precompiles dict instead of asserting
it's empty. -->
- [x] #55567 <!-- Initialize threadpools correctly during sysimg build
-->
- [x] #55596 <!-- Fast bounds-check for CartesianIndex ranges -->
- [x] #55605 <!-- Reroute Symmetric/Hermitian + Diagonal through
triangular -->
- [x] #55640 <!-- win: move stack_overflow_warning to the backtrace
fiber -->
- [x] #55715 <!-- Add precompile signatures to Markdown to reduce
latency. -->
- [x] #55593 <!-- Fix invalidations for FileIO -->
- [x] #55555 <!-- Revert "Don't expose guard pages to malloc_stack API
consumers" -->
- [x] #55720 <!-- Fix `pkgdir` for extensions -->
- [x] #55729 <!-- Avoid confounding compilation side effects of
`@time_imports` -->
- [x] #55718 <!-- Fix `@time_imports` extension recognition -->
- [x] #55522 <!-- Fix tr for Symmetric/Hermitian block matrices -->

Contains multiple commits, manual intervention needed:
- [ ] #55509 <!-- Fix cong implementation to be properly random and not
just cycling. -->

Non-merged PRs with backport label:
- [ ] #55641 <!-- fall back to slower stat filesize if optimized
filesize fails -->
- [ ] #55534 <!-- Set stdlib sources as read-only during installation
-->
- [ ] #55499 <!-- propagate the terminal's `displaysize` to the
`IOContext` used by the REPL -->
- [ ] #55458 <!-- Allow for generically extracting unannotated string
-->
- [ ] #55457 <!-- Make AnnotateChar equality consider annotations -->
- [ ] #55453 <!-- Privatise the annotations API, for StyledStrings -->
- [ ] #55355 <!-- relocation: account for trailing path separator in
depot paths -->
- [ ] #55220 <!-- `isfile_casesensitive` fixes on Windows -->
- [ ] #55169 <!-- `propertynames` for SVD respects private argument -->
- [ ] #54457 <!-- Make `String(::Memory)` copy -->
- [ ] #53957 <!-- tweak how filtering is done for what packages should
be precompiled -->
- [ ] #51479 <!-- prevent code loading from lookin in the versioned
environment when building Julia -->
- [ ] #50813 <!-- More doctests for Sockets and capitalization fix -->
- [ ] #50157 <!-- improve docs for `@inbounds` and
`Base.@propagate_inbounds` -->
- [ ] #41244 <!-- Fix shell `cd` error when working dir has been deleted
-->