for better cost estimation in the following series for matches.

Unfortunately, this does not necessarily result in better compression.
Results are all over the places,
with best outcome observed for silesia/x-ray
but most other files tend to get slightly worse after this change.

It's strange because it seems that we are just providing more accurate information for the cost estimator.

Anyway, as it also increases code complexity,
it's probably not interesting enough for now.

[license] Fix license header of huf_decompress_amd64.S

* Add the license header for `huf_decompress_amd64.S`
* Add `.S` files to the `test-license.py` test

[opt] Fix oss-fuzz bug in optimal parser

Remove Dependencies to Allow the Zstd Binary to Dynamically Link to the Library

oss-fuzz uncovered a scenario where we're evaluating the cost of litLength = 131072,
which can't be represented in the zstd format, so we accessed 1 beyond LL_bits.

Fix the issue by making it cost 1 bit more than litLength = 131071.

There are still follow ups:
1. This happened because literals_cost[0] = 0, so the optimal parser chose 36 literals
   over a match. Should we bound literals_cost[literal] > 0, unless the block truly only
   has one literal value?
2. When no matches are found, the cost model isn't updated. In this case no matches were
   found for an entire block. So the literals cost model wasn't updated at all. That made
   the optimal parser think literals_cost[0] = 0, where it is actually quite high, since
   the block was entirely random noise.

Credit to OSS-Fuzz.

xxHash symbols are present in `libzstd.so`, but they are local and therefore
unavailable outside the lib. There are two possible solutions to the problem.
We could make those symbols global, or we could remove the dependency.

This commit chooses the latter approach. I suppose this comes at the cost of
code size / build time. I'm open to comments on whether this is a good thing
to do, especially since this will apply even when we are statically linking
everything.

Improve Module Map File

This commit makes several changes:

1. It adds modules for the dictionary builder and errors headers.
2. It captures all of the macros that are used to configure these headers.
   When the headers are imported as modules and one of these macros is defined
   the compiler issues a warning that it needs to be defined on the CLI.
3. It promotes the modulemap file into the root of the lib directory.
   Experimentation shows that clang's `-fimplicit-module-maps` will find the
   modulemap when placed here, but not when it's put in a subdirectory.

Mark Huffman Decoder Assembly `noexecstack` on All Architectures

Previously we did this only on Linux, which missed other Unices.

Hopefully this marks the binary artifacts `noexecstack` even on platforms
where binaries default to true.

[meson] Explicitly disable assembly for non clang/gcc copmilers

fix performance issue in scenario #2966 (part 1)

After merging #2951 I realized that we will want to explicitly disable
assembly when we aren't including the assembly source file. Otherwise,
if some non clang/gcc compiler does support assembly, it would fail to
build.

meson: fix MSVC support

When re-using a compression state, across multiple successive compressions,
the state should minimize the amount of allocation and initialization required.

This mostly matters in situations where initialization is an overwhelming task
compared to compression itself.
This can happen when the amount to compress is small,
while the compression state was given the impression that it would be much larger,
aka, streaming mode without providing a srcSize hint.

This lean-initialization optimization was broken in 980f3bbf .

This commit fixes it, making this scenario once again on par with v1.4.9.

Note that this does not completely fix #2966,
since another heavy initialization, specific to row mode,
is also happening (and was not present in v1.4.9).
This will be fixed in a separate commit.

Apparently, even when the assembly file is empty (because
`ZSTD_ENABLE_ASM_X86_64_BMI2` is false), it still is marked as possibly
needing an executable stack and so the whole library is marked as such. This
commit applies a simple patch for this problem by moving the noexecstack
indication outside the macro guard.

This commit builds on #2857.

This commit addresses #2963.

Refactor offset+repcode sumtype 

Fix mini typo

storeSeq & mlBase : clarity refactoring

the new contracts seems to make more sense :
updateRep() updates an array of repeat offsets _in place_,
while newRep() generates a new structure with the updated repeat-offset array.

Most callers are actually expecting the in-place variant,
and a limited sub-section, in `zstd_opt.c` mainly, prefer `newRep()`.