Id::Invalid -> Id::None (#4834)

High level, replacing `Id::Invalid` with `Id::None` and `Id::is_valid`
with `Id::has_value` for clarity, as discussed
[here](https://discord.com/channels/655572317891461132/655578254970716160/1331664574545395794).
The `IntId` refactoring is needed together with `AnyIdBase` because it's
also used with `ValueStore`.

Note, trying to be careful not to rewrite `EnumBase::InvalidIndex`, or
`is_valid` in general (e.g., `IdKind::is_valid`).

I've tried to sequence commits here:

1. Automatic replacements:

- `((?:Id|Index)(?: |::|\(|Base(?:\(|::)))Invalid((?:Index)?\W)` ->
`$1None$2`
  - `<invalid>` -> `<none>`
  - `InvalidNodeId` -> `NoneNodeId`
  - `/\*invalid\*/` -> `/*none*/`
  - `id((?:_|\(\))(?:\.|->))is_valid` -> `id$1has_value`

2. Manual edits:

  - In `int.h` and `int_test.cpp`
    - `IntT` has `is_value`, which I'm renaming to `is_embedded_value`.
    - Manual edits to comments in this file.
  - `AnyIdBase` and `IdBase`
- Declaration of `is_valid` -> `has_value`, `InvalidIndex` ->
`NoneIndex`.
  - In `ids.h` and `ids.cpp`
    - `is_valid` -> `has_value`
- `// An explicitly invalid ID.` -> `// An ID with no value.`; similar
for index
    - Various math on `InvalidIndex` -> `NoneIndex`
    - Various mentions of "valid" in comments
  - In `value_store.h`, for `IdT::Invalid`, plus one comment
- In `impl.h` and `tokenized_buffer.h`, we had different initialization
of `::None` values (versus `ids.h` syntax) that I fixed manually.
  - Spot checks to compile
- Particularly where `is_valid` replacements didn't catch spots due to
different naming.

3. Autoupdate tests

4. verbose.carbon (NOAUTOUPDATE)

5. Comment spot checks

Note there are probably other mentions of "Invalid" that should be swept
up, but I'd like to argue for merging and separating out remaining
cleanup since this is so sweeping (and likely to hit merge conflicts
from churn). We'll probably have lingering mentions of "invalid" for a
bit regardless, just because there are uses of "invalid" in non-Id APIs.

toolchain/sem_ir/function.cpp

@@ -11,10 +11,10 @@
 namespace Carbon::SemIR {
 
 auto GetCalleeFunction(const File& sem_ir, InstId callee_id) -> CalleeFunction {
-  CalleeFunction result = {.function_id = FunctionId::Invalid,
-                           .enclosing_specific_id = SpecificId::Invalid,
-                           .resolved_specific_id = SpecificId::Invalid,
-                           .self_id = InstId::Invalid,
+  CalleeFunction result = {.function_id = FunctionId::None,
+                           .enclosing_specific_id = SpecificId::None,
+                           .resolved_specific_id = SpecificId::None,
+                           .self_id = InstId::None,
                            .is_error = false};
 
   if (auto specific_function =
@@ -30,7 +30,7 @@ auto GetCalleeFunction(const File& sem_ir, InstId callee_id) -> CalleeFunction {
 
   // Identify the function we're calling.
   auto val_id = sem_ir.constant_values().GetConstantInstId(callee_id);
-  if (!val_id.is_valid()) {
+  if (!val_id.has_value()) {
     return result;
   }
   auto val_inst = sem_ir.insts().Get(val_id);
@@ -87,7 +87,7 @@ auto Function::GetNameFromPatternId(const File& sem_ir, InstId pattern_id)
   }
 
   if (inst_id == SemIR::ErrorInst::SingletonInstId) {
-    return SemIR::NameId::Invalid;
+    return SemIR::NameId::None;
   }
 
   auto param_pattern_inst = inst.As<SemIR::AnyParamPattern>();
@@ -104,8 +104,8 @@ auto Function::GetNameFromPatternId(const File& sem_ir, InstId pattern_id)
 
 auto Function::GetDeclaredReturnType(const File& file,
                                      SpecificId specific_id) const -> TypeId {
-  if (!return_slot_pattern_id.is_valid()) {
-    return TypeId::Invalid;
+  if (!return_slot_pattern_id.has_value()) {
+    return TypeId::None;
   }
   return GetTypeInSpecific(file, specific_id,
                            file.insts().Get(return_slot_pattern_id).type_id());