BaseTools/VfrCompile: Fix potential buffer overwrites

While more portable methods exist to handle these cases, this change
does not attempt to do more than fix the immediate problem and
follow the conventions already established in this code.

`snprintf()` is introduced as the minimum improvement apart from
making the buffers larger.

Fixes the following CodeQL alerts:

1. Failure on line 2339 in
   BaseTools/Source/C/VfrCompile/Pccts/antlr/gen.c

   - Type: Potentially overrunning write
   - Severity: Critical
   - Problem: This 'call to sprintf' operation requires 17 bytes but
     the destination is only 16 bytes.

2. Failure on line 2341 in
   BaseTools/Source/C/VfrCompile/Pccts/antlr/gen.c

   - Type: Potentially overrunning write
   - Severity: Critical
   - Problem: This 'call to sprintf' operation requires 17 bytes but
     the destination is only 16 bytes.

3. Failure on line 1309 in
   BaseTools/Source/C/VfrCompile/Pccts/antlr/main.c

   - Type: Potentially overrunning write
   - Severity: Critical
   - Problem: This 'call to sprintf' operation requires 25 bytes but
     the destination is only 20 bytes.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Yuwei Chen <yuwei.chen@intel.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Oliver Smith-Denny <osd@smith-denny.com>