feat: add inheritable-only field to filter processor-level targets (#5270)

* feat: add inheritable-only field to hide processor-level targets from listing

Processor-level targets like esp32, rp2040, etc. have flash-method set
so they leak through the existing heuristic filter in GetTargetSpecs and
appear in `tinygo targets` output. Add an "inheritable-only" JSON field
that is checked on raw JSON before inheritance resolution, preventing
these non-board targets from being listed while keeping them loadable
for direct builds and inheritance.

Ref: tinygo-org/tinygo#5178

* fix: prevent inheritable-only from propagating to child targets

The InheritableOnly bool field was propagating from parent to child
targets through overrideProperties, which would hide board targets
from GetTargetSpecs. Fix by preserving/restoring the field across
resolveInherits. Also simplify GetTargetSpecs by removing the raw
JSON pre-check workaround and remove nonexistent esp32c6 from tests.

* prevent build commands to use inheritable only targets

targets/esp32.json

@@ -1,5 +1,6 @@
 {
 	"inherits": ["xtensa"],
+	"inheritable-only": true,
 	"cpu": "esp32",
 	"features": "+atomctl,+bool,+clamps,+coprocessor,+debug,+density,+dfpaccel,+div32,+exception,+fp,+highpriinterrupts,+interrupt,+loop,+mac16,+memctl,+minmax,+miscsr,+mul32,+mul32high,+nsa,+prid,+regprotect,+rvector,+s32c1i,+sext,+threadptr,+timerint,+windowed",
 	"build-tags": ["esp32", "esp"],

targets/esp32c3.json

@@ -1,5 +1,6 @@
 {
 	"inherits": ["riscv32"],
+	"inheritable-only": true,
 	"features": "+32bit,+c,+m,+zmmul,-a,-b,-d,-e,-experimental-sdext,-experimental-sdtrig,-experimental-smctr,-experimental-ssctr,-experimental-svukte,-experimental-xqcia,-experimental-xqciac,-experimental-xqcicli,-experimental-xqcicm,-experimental-xqcics,-experimental-xqcicsr,-experimental-xqciint,-experimental-xqcilo,-experimental-xqcilsm,-experimental-xqcisls,-experimental-zalasr,-experimental-zicfilp,-experimental-zicfiss,-experimental-zvbc32e,-experimental-zvkgs,-f,-h,-relax,-sha,-shcounterenw,-shgatpa,-shtvala,-shvsatpa,-shvstvala,-shvstvecd,-smaia,-smcdeleg,-smcsrind,-smdbltrp,-smepmp,-smmpm,-smnpm,-smrnmi,-smstateen,-ssaia,-ssccfg,-ssccptr,-sscofpmf,-sscounterenw,-sscsrind,-ssdbltrp,-ssnpm,-sspm,-ssqosid,-ssstateen,-ssstrict,-sstc,-sstvala,-sstvecd,-ssu64xl,-supm,-svade,-svadu,-svbare,-svinval,-svnapot,-svpbmt,-svvptc,-v,-xcvalu,-xcvbi,-xcvbitmanip,-xcvelw,-xcvmac,-xcvmem,-xcvsimd,-xesppie,-xmipscmove,-xmipslsp,-xsfcease,-xsfvcp,-xsfvfnrclipxfqf,-xsfvfwmaccqqq,-xsfvqmaccdod,-xsfvqmaccqoq,-xsifivecdiscarddlone,-xsifivecflushdlone,-xtheadba,-xtheadbb,-xtheadbs,-xtheadcmo,-xtheadcondmov,-xtheadfmemidx,-xtheadmac,-xtheadmemidx,-xtheadmempair,-xtheadsync,-xtheadvdot,-xventanacondops,-xwchc,-za128rs,-za64rs,-zaamo,-zabha,-zacas,-zalrsc,-zama16b,-zawrs,-zba,-zbb,-zbc,-zbkb,-zbkc,-zbkx,-zbs,-zca,-zcb,-zcd,-zce,-zcf,-zcmop,-zcmp,-zcmt,-zdinx,-zfa,-zfbfmin,-zfh,-zfhmin,-zfinx,-zhinx,-zhinxmin,-zic64b,-zicbom,-zicbop,-zicboz,-ziccamoa,-ziccif,-zicclsm,-ziccrse,-zicntr,-zicond,-zicsr,-zifencei,-zihintntl,-zihintpause,-zihpm,-zimop,-zk,-zkn,-zknd,-zkne,-zknh,-zkr,-zks,-zksed,-zksh,-zkt,-ztso,-zvbb,-zvbc,-zve32f,-zve32x,-zve64d,-zve64f,-zve64x,-zvfbfmin,-zvfbfwma,-zvfh,-zvfhmin,-zvkb,-zvkg,-zvkn,-zvknc,-zvkned,-zvkng,-zvknha,-zvknhb,-zvks,-zvksc,-zvksed,-zvksg,-zvksh,-zvkt,-zvl1024b,-zvl128b,-zvl16384b,-zvl2048b,-zvl256b,-zvl32768b,-zvl32b,-zvl4096b,-zvl512b,-zvl64b,-zvl65536b,-zvl8192b",
 	"build-tags": ["esp32c3", "esp"],
 	"serial": "usb",

targets/esp32s3.json

@@ -1,5 +1,6 @@
 {
 	"inherits": ["xtensa"],
+	"inheritable-only": true,
 	"cpu": "esp32s3",
 	"features": "+atomctl,+bool,+clamps,+coprocessor,+debug,+density,+div32,+esp32s3,+exception,+fp,+highpriinterrupts,+interrupt,+loop,+mac16,+memctl,+minmax,+miscsr,+mul32,+mul32high,+nsa,+prid,+regprotect,+rvector,+s32c1i,+sext,+threadptr,+timerint,+windowed",
 	"build-tags": ["esp32s3", "esp"],

targets/esp8266.json

@@ -1,5 +1,6 @@
 {
 	"inherits": ["xtensa"],
+	"inheritable-only": true,
 	"cpu": "esp8266",
 	"features": "+debug,+density,+exception,+extendedl32r,+highpriinterrupts,+interrupt,+mul32,+nsa,+prid,+regprotect,+rvector,+timerint",
 	"build-tags": ["esp8266", "esp"],

targets/rp2040.json

@@ -1,5 +1,6 @@
 {
     "inherits": ["cortex-m0plus"],
+    "inheritable-only": true,
     "build-tags": ["rp2040", "rp"],
     "scheduler": "tasks",
     "flash-1200-bps-reset": "true",

targets/rp2350.json

@@ -1,5 +1,6 @@
 {
     "inherits": ["cortex-m33"],
+    "inheritable-only": true,
     "build-tags": ["rp2350", "rp"],
     "scheduler": "tasks",
     "flash-1200-bps-reset": "true",

targets/rp2350b.json

@@ -1,5 +1,6 @@
 {
     "inherits": ["rp2350"],
+    "inheritable-only": true,
     "build-tags": ["rp2350b"],
     "serial-port": ["2e8a:000f"]
 }