Migrate all CARBON_VLOG to the format string variant. (#4284)

This mostly uses a hilarious set of regular expressions to mechanically
switch all but two uses, and then manually fixed the last two. There
weren't too many.

Also simplifies the `vlog` implementation now that it's all going
through a format string.

This alone has a nice impact on parse and check of about 2% and 1%
respectively. The impact on lex in my timings looks like noise (no
change in instruction count, unlike the other phases).
```
name                                               old cpu/op   new cpu/op   delta
BM_CompileAPIFileDenseDecls<Phase::Lex>/256        39.1µs ± 3%  38.1µs ± 2%  -2.42%  (p=0.000 n=20+19)
BM_CompileAPIFileDenseDecls<Phase::Lex>/1024        187µs ± 3%   183µs ± 1%  -2.30%  (p=0.000 n=20+20)
BM_CompileAPIFileDenseDecls<Phase::Lex>/4096        776µs ± 4%   756µs ± 1%  -2.62%  (p=0.000 n=20+20)
BM_CompileAPIFileDenseDecls<Phase::Lex>/16384      3.36ms ± 1%  3.33ms ± 1%  -0.90%  (p=0.000 n=18+18)
BM_CompileAPIFileDenseDecls<Phase::Lex>/65536      14.4ms ± 2%  14.2ms ± 1%  -1.41%  (p=0.000 n=20+20)
BM_CompileAPIFileDenseDecls<Phase::Lex>/262144     65.7ms ± 1%  65.2ms ± 2%  -0.86%  (p=0.002 n=19+20)
BM_CompileAPIFileDenseDecls<Phase::Parse>/256      87.5µs ± 1%  86.3µs ± 1%  -1.43%  (p=0.000 n=19+20)
BM_CompileAPIFileDenseDecls<Phase::Parse>/1024      438µs ± 2%   431µs ± 1%  -1.54%  (p=0.000 n=19+20)
BM_CompileAPIFileDenseDecls<Phase::Parse>/4096     1.81ms ± 2%  1.77ms ± 1%  -2.12%  (p=0.000 n=20+20)
BM_CompileAPIFileDenseDecls<Phase::Parse>/16384    7.54ms ± 1%  7.43ms ± 1%  -1.44%  (p=0.000 n=19+20)
BM_CompileAPIFileDenseDecls<Phase::Parse>/65536    31.2ms ± 1%  30.6ms ± 1%  -2.03%  (p=0.000 n=20+20)
BM_CompileAPIFileDenseDecls<Phase::Parse>/262144    133ms ± 1%   130ms ± 1%  -1.85%  (p=0.000 n=20+20)
BM_CompileAPIFileDenseDecls<Phase::Check>/256       882µs ± 1%   878µs ± 1%  -0.52%  (p=0.001 n=17+19)
BM_CompileAPIFileDenseDecls<Phase::Check>/1024     1.90ms ± 2%  1.88ms ± 1%  -1.17%  (p=0.000 n=19+19)
BM_CompileAPIFileDenseDecls<Phase::Check>/4096     5.85ms ± 2%  5.76ms ± 1%  -1.43%  (p=0.000 n=20+19)
BM_CompileAPIFileDenseDecls<Phase::Check>/16384    22.2ms ± 2%  21.9ms ± 2%  -1.20%  (p=0.000 n=20+19)
BM_CompileAPIFileDenseDecls<Phase::Check>/65536    91.2ms ± 2%  90.3ms ± 1%  -1.00%  (p=0.000 n=20+19)
BM_CompileAPIFileDenseDecls<Phase::Check>/262144    382ms ± 1%   380ms ± 1%  -0.51%  (p=0.003 n=18+19)
```

toolchain/check/inst_block_stack.cpp

@@ -11,7 +11,7 @@
 namespace Carbon::Check {
 
 auto InstBlockStack::Push(SemIR::InstBlockId id) -> void {
-  CARBON_VLOG() << name_ << " Push " << id_stack_.size() << "\n";
+  CARBON_VLOG("{0} Push {1}\n", name_, id_stack_.size());
   CARBON_CHECK(id_stack_.size() < (1 << 20))
       << "Excessive stack size: likely infinite loop";
   id_stack_.push_back(id);
@@ -50,7 +50,7 @@ auto InstBlockStack::Pop() -> SemIR::InstBlockId {
 
   insts_stack_.PopArray();
 
-  CARBON_VLOG() << name_ << " Pop " << id_stack_.size() << ": " << id << "\n";
+  CARBON_VLOG("{0} Pop {1}: {2}\n", name_, id_stack_.size(), id);
   return id.is_valid() ? id : SemIR::InstBlockId::Empty;
 }
 
@@ -58,7 +58,7 @@ auto InstBlockStack::PopAndDiscard() -> void {
   CARBON_CHECK(!empty()) << "no current block";
   id_stack_.pop_back();
   insts_stack_.PopArray();
-  CARBON_VLOG() << name_ << " PopAndDiscard " << id_stack_.size() << "\n";
+  CARBON_VLOG("{0} PopAndDiscard {1}\n", name_, id_stack_.size());
 }
 
 auto InstBlockStack::PrintForStackDump(SemIR::Formatter& formatter, int indent,